4. PLEAC Julia: Arrays¶

PLEAC = Language Examples Alike Cookbook PLEAC examples are drawn from the "Perl Cookbook" by Tom Christiansen & Nathan Torkington, published by O'Reilly. They provide a nice range of examples oriented toward data munging, the type of work I tend to want to do first when learning a new language.

The Julia examples below are principally translations from the Python version

Caution¶

I'm learning as I go, so the code below probably doesn't represent best practice. Your suggestions are welcome! Please file an issue or make a pull request to the github repo.

The examples are not complete. Missing items are generally noted in comments.

PLEAC 4.1: Introduction¶

Julia provides 2 major types of Arrays, typed arrays and arrays of Any (aka cell arrays). Cell arrays can contain arbitrary types, including nested arrays. Typed arrays are automatically flattened.

In [1]:

non_nested = ["this", "that", "the", "other"]'

Out[1]:

1x4 Array{ASCIIString,2}:
 "this"  "that"  "the"  "other"

In [2]:

nested_typed = ["this", "that", ["the", "other"]]'

Out[2]:

1x4 Array{ASCIIString,2}:
 "this"  "that"  "the"  "other"

In [3]:

nested_cell = {"this", "that", ["the", "other"]}'

Out[3]:

1x3 Array{Any,2}:
 "this"  "that"  ["the","other"]

In [4]:

tune = ["The", "Star-Spangled", "Banner"]'

Out[4]:

1x3 Array{ASCIIString,2}:
 "The"  "Star-Spangled"  "Banner"

In [5]:

Vector[1,4,6]

WARNING:

no method convert(Type{Array{T,1}},Int64)
at In[5]:1
 in setindex! at array.jl:412
 in getindex at array.jl:153

PLEAC 4.2 Specifying an array in your program¶

In [6]:

a = ["quick", "brown", "fox"]'

backtraces on your platform are often misleading or partially incorrect

Out[6]:

1x3 Array{ASCIIString,2}:
 "quick"  "brown"  "fox"

In [7]:

a = split("Why are you teasing me?")'

Out[7]:

1x5 Array{String,2}:
 "Why"  "are"  "you"  "teasing"  "me?"

In [8]:

text = """
    The boy stood on the burning deck,
    It was as hot as glass.
"""

Out[8]:

"    The boy stood on the burning deck,\n    It was as hot as glass.\n"

In [9]:

lines = [strip(l) for l in split(strip(text),'\n')]

Out[9]:

2-element Array{Any,1}:
 "The boy stood on the burning deck,"
 "It was as hot as glass."

In [10]:

sio = IOBuffer(text)  # using iobuffer rather than file here

Out[10]:

IOBuffer([0x20,0x20,0x20,0x20,0x54,0x68,0x65,0x20,0x62,0x6f  …  0x61,0x73,0x20,0x67,0x6c,0x61,0x73,0x73,0x2e,0x0a],true,false,true,false,67,9223372036854775807,1)

In [11]:

tl=readlines(sio)
sl=[strip(l) for l in tl]

Out[11]:

2-element Array{Any,1}:
 "The boy stood on the burning deck,"
 "It was as hot as glass."

In [12]:

close(sio)

In [13]:

banner = "The Mines of Moria"
#no single quoted strings in Julia
name = "Gandalf"
banner = "Speak,$name and enter!"

Out[13]:

"Speak,Gandalf and enter!"

In [14]:

@sprintf("Speak, %s, and welcome!", name)

Out[14]:

"Speak, Gandalf, and welcome!"

In [15]:

his_host = "www.julialang.org"
getaddrinfo(his_host)

Out[15]:

ip"204.232.175.78"

In [16]:

julia_info=getpid() # Julia's process id

Out[16]:

In [17]:

#shell_info
;tasklist 

Image Name                     PID Session Name        Session#    Mem Usage
========================= ======== ================ =========== ============
System Idle Process              0 Services                   0         24 K
System                           4 Services                   0      6,280 K
smss.exe                       388 Services                   0        712 K
csrss.exe                      488 Services                   0      4,000 K
wininit.exe                    572 Services                   0      1,396 K
csrss.exe                      584 Console                    1     61,912 K
winlogon.exe                   636 Console                    1      3,344 K
services.exe                   656 Services                   0     14,328 K
lsass.exe                      684 Services                   0     20,524 K
lsm.exe                        692 Services                   0      4,432 K
svchost.exe                    788 Services                   0      7,176 K
svchost.exe                    864 Services                   0     14,076 K
svchost.exe                    948 Services                   0     20,464 K
svchost.exe                    980 Services                   0     18,604 K
svchost.exe                   1012 Services                   0     25,360 K
svchost.exe                    156 Services                   0     48,920 K
stacsv64.exe                   496 Services                   0      5,956 K
svchost.exe                   1092 Services                   0      8,680 K
Prot_srv.exe                  1236 Services                   0     17,756 K
vpnagent.exe                  1388 Services                   0      9,880 K
svchost.exe                   1432 Services                   0     27,468 K
EvtEng.exe                    1524 Services                   0      5,824 K
ZCfgSvc7.exe                  1628 Services                   0      5,064 K
spoolsv.exe                   1704 Services                   0     29,176 K
ac.sharedstore.exe            1732 Services                   0      3,580 K
HostControlService.exe        1768 Services                   0      2,380 K
acevents.exe                  1776 Services                   0      4,480 K
HostStorageService.exe        1800 Services                   0      2,208 K
svchost.exe                   1824 Services                   0      8,472 K
svchost.exe                   1864 Services                   0     10,972 K
armsvc.exe                    1968 Services                   0      1,900 K
AESTSr64.exe                  1992 Services                   0      1,384 K
AeXNSAgent.exe                2020 Services                   0      9,188 K
AgentService.exe              1964 Services                   0     27,192 K
unsecapp.exe                  2084 Services                   0      2,176 K
WmiPrvSE.exe                  2160 Services                   0      5,884 K
svchost.exe                   2264 Services                   0      5,972 K
svchost.exe                   2296 Services                   0      3,040 K
LGVL600SVC.exe                2428 Services                   0      2,148 K
schsvc.exe                    2560 Services                   0     51,532 K
sqlservr.exe                  2672 Services                   0     35,500 K
o2flash.exe                   2724 Services                   0      2,752 K
srvany.exe                    2768 Services                   0      1,324 K
SDIOAssist.exe                2844 Services                   0      3,008 K
PDFProFiltSrvPP.exe           2964 Services                   0      1,724 K
pstartSr.exe                  3028 Services                   0      2,052 K
pg_ctl.exe                    3068 Services                   0      1,900 K
radexecd.exe                  1280 Services                   0      2,920 K
radstgms.exe                  2580 Services                   0      2,600 K
RegSrvc.exe                   3080 Services                   0      2,420 K
postgres.exe                  3088 Services                   0     36,292 K
conhost.exe                   3096 Services                   0      1,116 K
upeksvr.exe                   3148 Console                    1      7,112 K
ccSvcHst.exe                  3156 Services                   0     20,884 K
sqlwriter.exe                 3240 Services                   0      8,616 K
postgres.exe                  3272 Services                   0      1,848 K
svchost.exe                   3280 Services                   0     19,088 K
tvnserver.exe                 3412 Services                   0      2,908 K
svchost.exe                   3452 Services                   0      4,444 K
postgres.exe                  3464 Services                   0      1,752 K
postgres.exe                  3472 Services                   0      3,292 K
postgres.exe                  3488 Services                   0      1,676 K
postgres.exe                  3500 Services                   0      2,552 K
postgres.exe                  3516 Services                   0      1,940 K
WLIDSVC.EXE                   3540 Services                   0      5,852 K
WLIDSVCM.EXE                  3816 Services                   0      1,292 K
taskhost.exe                  4128 Console                    1      7,996 K
ccSvcHst.exe                  4148 Console                    1      5,256 K
dwm.exe                       4436 Console                    1      3,764 K
explorer.exe                  4508 Console                    1    109,804 K
acevents.exe                  4864 Console                    1      5,556 K
accrdsub.exe                  4984 Console                    1      7,324 K
Smc.exe                       5016 Services                   0     20,564 K
Apoint.exe                    5088 Console                    1      5,280 K
iFrmewrk.exe                  5140 Console                    1      7,316 K
sttray64.exe                  5148 Console                    1      5,648 K
FF_Protection.exe             5256 Console                    1      3,104 K
tvnserver.exe                 5268 Console                    1      2,464 K
MSOSYNC.EXE                   5320 Console                    1      7,928 K
ISUSPM.exe                    5352 Console                    1      8,496 K
acsagent.exe                  5400 Console                    1      5,944 K
ONENOTEM.EXE                  5428 Console                    1      1,120 K
RoxioBurnLauncher.exe         5588 Console                    1      4,944 K
PDVD9Serv.exe                 5612 Console                    1      2,224 K
svchost.exe                   5700 Services                   0      3,244 K
AeXNSAgentHostSurrogate32     5740 Services                   0     12,108 K
IAStorIcon.exe                5924 Console                    1     11,648 K
WUDFHost.exe                  6084 Services                   0      2,288 K
schTray.exe                   5296 Console                    1     21,084 K
cptray.exe                    5640 Console                    1      2,608 K
ApMsgFwd.exe                  6244 Console                    1      1,852 K
ApntEx.exe                    6436 Console                    1      3,332 K
hidfind.exe                   6448 Console                    1      2,156 K
conhost.exe                   6480 Console                    1      2,196 K
P95tray.exe                   6536 Console                    1      3,828 K
unsecapp.exe                  6580 Console                    1      3,272 K
Agent.exe                     6716 Console                    1    270,748 K
AeXAgentUIHost.exe            6852 Console                    1      4,596 K
pptd40nt.exe                  6956 Console                    1      2,456 K
pdfPro5Hook.exe               6972 Console                    1      2,120 K
SearchIndexer.exe             1312 Services                   0     75,824 K
BrStMonW.exe                  6048 Console                    1    231,044 K
BrCtrlCntr.exe                6732 Console                    1      1,944 K
vpnui.exe                     6676 Console                    1     16,980 K
BrYNSvc.exe                   6684 Services                   0      5,012 K
communicator.exe              7028 Console                    1     87,976 K
EMET_Agent.exe                7044 Console                    1     17,692 K
BrCcUxSys.exe                 7328 Console                    1      2,200 K
PrivacyIconClient.exe         8584 Console                    1     24,968 K
LMS.exe                       8620 Services                   0      3,792 K
UNS.exe                       8644 Services                   0      9,708 K
UcMapi.exe                    8844 Console                    1     41,736 K
IAStorDataMgrSvc.exe          4924 Services                   0      9,396 K
OSPPSVC.EXE                   2660 Services                   0     10,696 K
wmpnetwk.exe                 11340 Services                   0     11,668 K
ielowutil.exe                 1040 Console                    1      1,256 K
TGitCache.exe                 5408 Console                    1     15,512 K
chrome.exe                   11416 Console                    1    765,144 K
chrome.exe                    9876 Console                    1    106,112 K
splwow64.exe                  9096 Console                    1     19,604 K
JuniperSetupClient.exe       13044 Console                    1     16,564 K
svchost.exe                   1820 Services                   0      5,336 K
notepad++.exe                10576 Console                    1     39,184 K
WmiPrvSE.exe                  1556 Services                   0     32,232 K
chrome.exe                    5912 Console                    1     11,268 K
ssh-agent.exe                 7040 Console                    1      4,876 K
SearchProtocolHost.exe       12760 Services                   0     11,216 K
WINWORD.EXE                  14156 Console                    1    139,064 K
chrome.exe                    6904 Console                    1    106,924 K
chrome.exe                   13828 Console                    1     43,144 K
chrome.exe                    9188 Console                    1     46,628 K
chrome.exe                   12196 Console                    1     51,828 K
chrome.exe                   10204 Console                    1     44,560 K
chrome.exe                    1960 Console                    1     64,488 K
WmiPrvSE.exe                 10480 Services                   0     21,892 K
svchost.exe                   5764 Services                   0      5,940 K
chrome.exe                    7944 Console                    1     56,768 K
OUTLOOK.EXE                   8352 Console                    1    193,008 K
python.exe                    9048 Console                    1     64,496 K
conhost.exe                  10516 Console                    1      8,844 K
chrome.exe                    8100 Console                    1     78,688 K
cmd.exe                       7372 Console                    1      3,616 K
julia-readline.exe            8516 Console                    1    287,812 K
cmd.exe                      12060 Console                    1      3,616 K
julia-readline.exe            8272 Console                    1    150,012 K
cmd.exe                      12936 Console                    1      3,448 K
conhost.exe                   5728 Console                    1      8,840 K
w3wp.exe                      4496 Services                   0     13,312 K
taskeng.exe                  12728 Services                   0      5,724 K
taskeng.exe                   8224 Console                    1      7,284 K
cmd.exe                      11232 Console                    1      3,656 K
julia-readline.exe            8872 Console                    1    284,336 K
chrome.exe                   12464 Console                    1     56,476 K
radsched.exe                  8148 Services                   0      5,512 K
SearchFilterHost.exe          4516 Services                   0      7,292 K
tasklist.exe                  7496 Console                    1      6,704 K

In [18]:

banner = ["Costs", "only", "$4.95"]'  # $ stripped due to substitution

Out[18]:

1x3 Array{ASCIIString,2}:
 "Costs"  "only"  "4.95"

In [19]:

banner = ["Costs", "only", "\$4.95"]'

Out[19]:

1x3 Array{ASCIIString,2}:
 "Costs"  "only"  "\$4.95"

In [20]:

print(banner[3])

$4.95

In [21]:

banner = split("Costs only \$4.95")'

Out[21]:

1x3 Array{String,2}:
 "Costs"  "only"  "\$4.95"

In [22]:

 brax=split(""" ' " ( ) < > { } [ ] """)'

Out[22]:

1x10 Array{String,2}:
 "'"  "\""  "("  ")"  "<"  ">"  "{"  "}"  "["  "]"

In [23]:

# no ''' in Julia

In [24]:

tags = split("LI TABLE TR TD A IMG H1 P")'

Out[24]:

1x8 Array{String,2}:
 "LI"  "TABLE"  "TR"  "TD"  "A"  "IMG"  "H1"  "P"

In [25]:

sample = split("The backslash (\\) is often used in regular expressions.")'

Out[25]:

1x9 Array{String,2}:
 "The"  "backslash"  "(\\)"  "is"  …  "in"  "regular"  "expressions."

In [26]:

#Julia uses Unicode by default, so no string qualifier is required
ships = "Niña Pinta Santa María"
split(ships)'

Out[26]:

1x4 Array{String,2}:
 "Niña"  "Pinta"  "Santa"  "María"

In [27]:

ships = ["Niña", "Pinta", "Santa María"]

Out[27]:

3-element Array{UTF8String,1}:
 "Niña"       
 "Pinta"      
 "Santa María"

PLEAC 4.3: Printing a list with commas¶

In [28]:

js=join(ships,", ")
js= length(ships)>1? replace(js,", "*ships[end], " and "*ships[end]) : js

Out[28]:

"Niña, Pinta and Santa María"

In [29]:

function commify_series(arr::Array)
    js=join(arr,", ")
    js=length(arr)>1? replace(js,", "*arr[end], " and "*arr[end]) : js
end

Out[29]:

commify_series (generic function with 1 method)

In [30]:

commify_series([])

Out[30]:

""

In [31]:

commify_series(["red"])

Out[31]:

"red"

In [32]:

commify_series(["red","yellow"]) 

Out[32]:

"red and yellow"

In [33]:

commify_series(["red","yellow","green"])

Out[33]:

"red, yellow and green"

In [34]:

myarray = ["red","yellow","green"]'

Out[34]:

1x3 Array{ASCIIString,2}:
 "red"  "yellow"  "green"

In [35]:

println( "I have [$(join(myarray,", "))] marbles." )

I have [red, yellow, green] marbles.

In [36]:

println( "I have " * join(myarray,' ') * " marbles." )

I have red yellow green marbles.

In [37]:

# commify_series - show proper comma insertion in list output
data = {
    ( "just one thing", ),
    ( split("Mutt Jeff") ),
    ( split("Peter Paul Mary") ),
    ( "To our parents", "Mother Theresa", "God" ),
    ( "pastrami", "ham and cheese", "peanut butter and jelly", "tuna" ),
    ( "recycle tired, old phrases", "ponder big, happy thoughts" ),
    ( "recycle tired, old phrases", "ponder big, happy thoughts", "sleep and dream peacefully" ),
    }

Out[37]:

7-element Array{Any,1}:
 ("just one thing",)                                                                     
 ["Mutt","Jeff"]                                                                         
 ["Peter","Paul","Mary"]                                                                 
 ("To our parents","Mother Theresa","God")                                               
 ("pastrami","ham and cheese","peanut butter and jelly","tuna")                          
 ("recycle tired, old phrases","ponder big, happy thoughts")                             
 ("recycle tired, old phrases","ponder big, happy thoughts","sleep and dream peacefully")

In [38]:

typeof(data)

Out[38]:

Array{Any,1}

In [39]:

function commify_sep(terms::Array)
    sep=", "
    for term in terms
        if "," in term
            sep = "; "
        end
    end   
    return sep
end

Out[39]:

commify_sep (generic function with 1 method)

In [40]:

for item in data
    #println(item)
    println("$(commify_sep(item)).")
end

no method commify_sep((ASCIIString,),)
at In[40]:4
 in anonymous at no file:3

In [41]:

function commify_series3(terms)
    sep = commify_sep(terms)
    n=length(terms)
    if n==0
        return ""
    elseif n==1
        return terms[1]
    elseif n==2
        return "$(terms[1]) and $(terms[2])"
    else
        return "$(join(terms[1:end-1],sep))$(sep)and $(terms[end])"
    end
end

Out[41]:

commify_series3 (generic function with 1 method)

In [42]:

for item in data
    println("The list is: $(commify_series3(item)).")
end

no method commify_sep((ASCIIString,),)
at In[42]:3
 in commify_series3 at In[41]:2

PLEAC 4.4: Changing Array Size¶

In [43]:

a = Array(Int,5)'

Out[43]:

1x5 Array{Int64,2}:
 57451264  62701552  74991088  67816400  74991280

In [44]:

#resize via assignment
mysize=3
a = a[1:mysize]
a'

Out[44]:

1x3 Array{Int64,2}:
 57451264  62701552  74991088

methods that change an object in-place usually end with !¶

In [45]:

# To add an element to the end of a list, use the push! method:
push!(a,4)
a'

Out[45]:

1x4 Array{Int64,2}:
 57451264  62701552  74991088  4

In [46]:

# To insert an element, use the insert! method:
insert!(a,1,10)
a'

Out[46]:

1x5 Array{Int64,2}:
 10  57451264  62701552  74991088  4

In [47]:

# To append one list with the contents of another, use the append! method
a2 = [ 1,2,3 ]
append!(a,a2)
a'

Out[47]:

1x8 Array{Int64,2}:
 10  57451264  62701552  74991088  4  1  2  3

In [48]:

# To insert the contents of one list into another, overwriting zero or 
# more elements, specify a slice
a[2:4] = a2
a'

Out[48]:

1x8 Array{Int64,2}:
 10  1  2  3  4  1  2  3

In [49]:

a[1]=0
a[2]=8
a'

Out[49]:

1x8 Array{Int64,2}:
 0  8  2  3  4  1  2  3

In [50]:

# To remove one element from the middle of a list
splice!(a,2)

Out[50]:

In [51]:

a'

Out[51]:

1x7 Array{Int64,2}:
 0  2  3  4  1  2  3

In [52]:

# To remove elements from the middle of a list:
splice!(a,3:5)'

Out[52]:

1x3 Array{Int64,2}:
 3  4  1

In [53]:

a'

Out[53]:

1x4 Array{Int64,2}:
 0  2  2  3

In [54]:

function what_about_that_array(terms)
    println( "The list now has $(length(terms)) elements.")
    println( "The index of the last element is $(length(terms))" )
    println( "Element #3 is $(terms[3])" )
end

Out[54]:

what_about_that_array (generic function with 1 method)

In [55]:

what_about_that_array(a)

The list now has 4 elements.
The index of the last element is 4
Element #3 is 2

In [56]:

terms=a
println( "The index of the last element is $(length(terms))" )

The index of the last element is 4

In [57]:

people = split("Crosby Stills Nash Young")

Out[57]:

4-element Array{String,1}:
 "Crosby"
 "Stills"
 "Nash"  
 "Young"

In [58]:

what_about_that_array(people)

The list now has 4 elements.
The index of the last element is 4
Element #3 is Nash

In [59]:

pop!(people)

Out[59]:

"Young"

In [60]:

what_about_that_array(people)

The list now has 3 elements.
The index of the last element is 3
Element #3 is Nash

In [60]:

sz=10000-length(people)
xtra=[None for i in 1:sz ];

In [60]:

append!(people, xtra);

no method convert(Type{String},UnionType)
at In[60]:1
 in copy! at abstractarray.jl:230

PLEAC 4.5 Doing something with every element in an array¶

In [61]:

myarray

Out[61]:

1x3 Array{ASCIIString,2}:
 "red"  "yellow"  "green"

In [62]:

for item in myarray
    pass
end

In [63]:

for (k,v) = ENV
    print( k, v[1:min(length(v),' ',6)], ' ' ) 
end

C:=c:\ COLUMNS80 JL_PRIVATE_LIBDIRbin JULIAC:\Tem JULIA_EDITORstart JULIA_EXEjulia- JULIA_HOMEC:\Tem LINES30 PROMPT$P$G SYS_PATHc:\pyt TMPC:\Use COMPUTERNAMEMM1911 USERDOMAINMITRE BURN_AUTOPLAYC:\Pro EMC_AUTOPLAYC:\Pro PSMODULEPATHC:\Win COMMONPROGRAMFILESC:\Pro PROCESSOR_IDENTIFIERIntel6 PROGRAMFILESC:\Pro PROCESSOR_REVISION2a07 GPHOME_CLIENTSC:\Pro PATHC:\Tem NUMBER_OF_PROCESSORS8 PROGRAMFILES(X86)C:\Pro WINDOWS_TRACING_FLAGS3 SSH_AGENT_PID1056 TK_LIBRARYC:\Pyt PRGC:\Pro GIT_SSHC:\Pro TEMPC:\Use ORACLE_HOMEC:\Ora COMMONPROGRAMFILES(X86)C:\Pro PROCESSOR_ARCHITECTUREAMD64 TIX_LIBRARYC:\Pyt ALLUSERSPROFILEC:\Pro TNS_ADMINC:\Ora LOCALAPPDATAC:\Use HOMEPATH\Users USERDOMAIN_ROAMINGPROFILEMITRE PROGRAMW6432C:\Pro USERNAMEKEITHC FP_NO_HOST_CHECKNO LOGONSERVER\\MBDC SYSTEMROOTC:\Win SESSIONNAMEConsol PROGRAMDATAC:\Pro PYTHONPATHC:\Pyt SSH_AUTH_SOCK/tmp/s TCL_LIBRARYC:\Pyt USERDNSDOMAINMITRE. R_HOMEC:\Pro PATHEXT.COM;. GDAL_DATAC:\Pro WINDIRC:\Win WINDOWS_TRACING_LOGFILEC:\BVT HOMEDRIVEC: RCAUTOPLAYC:\Pro SYSTEMDRIVEC: P86C:\Pro COMSPECC:\Win SVN_SSHC:\Pro APPDATAC:\Use PROCESSOR_LEVEL6 COMMONPROGRAMW6432C:\Pro OSWindow PUBLICC:\Use VTK_DATA_ROOTC:\Pyt USERPROFILEC:\Use

In [64]:

# skipped examples with get_usage() and who

In [65]:

mytext="""a frumpily godgered
  skillufous banger.
  nasbue u oiper 
  han yty poy"""
fakefile = IOBuffer(mytext)

Out[65]:

IOBuffer([0x61,0x20,0x66,0x72,0x75,0x6d,0x70,0x69,0x6c,0x79  …  0x61,0x6e,0x20,0x79,0x74,0x79,0x20,0x70,0x6f,0x79],true,false,true,false,66,9223372036854775807,1)

In [66]:

while ~eof(fakefile)
 ln=readline(fakefile)
 words = split(ln)
 for w in words
    print(reverse(w)*" ")
 end 
end

a ylipmurf deregdog suofulliks .regnab eubsan u repio nah yty yop

In [67]:

data = [1, 2, 3]'

Out[67]:

1x3 Array{Int64,2}:
 1  2  3

In [68]:

data = [i-1 for i in data]'

Out[68]:

1x3 Array{Any,2}:
 0  1  2

In [69]:

# skipped final example

PLEAC 4.6: Iterating over an array by reference¶

In [70]:

fruits = ["Apple", "Blackberry"]
for fruit in fruits
    println( fruit, " tastes good in a pie.")
end

Apple tastes good in a pie.
Blackberry tastes good in a pie.

In [71]:

# If you must explicitly index, use enumerate():
for (i, fruit) in enumerate(fruits)
        println( i,' ', fruit, " tastes good in a pie.")
end

1 Apple tastes good in a pie.
2 Blackberry tastes good in a pie.

In [72]:

rogue_cats = ["Morris", "Felix"]
namedict = { "felines"=> rogue_cats }

Out[72]:

{"felines"=>["Morris","Felix"]}

In [73]:

for cat in namedict["felines"]
    println( cat, "purrs hypnotically.")
end
println( "--More-- \nYou are controlled.")

Morrispurrs hypnotically.
Felixpurrs hypnotically.
--More-- 
You are controlled.

PLEAC 4.7: Extracting unique elements from a list¶

In [74]:

ar=[1,2,2,4,5,6,6]
unique(ar)'

Out[74]:

1x5 Array{Int64,2}:
 1  2  4  5  6

In [75]:

myset=Set(ar...)

Out[75]:

Set{Int64}(5,4,6,2,1)

In [76]:

seen=Dict()
for item in ar
   seen[item] = get(seen,item, 0) + 1
end
seen

Out[76]:

{5=>1,4=>1,6=>2,2=>2,1=>1}

In [77]:

uniq=[k for k in keys(seen)]
uniq'

Out[77]:

1x5 Array{Any,2}:
 5  4  6  2  1

In [78]:

# generate a list of users logged in, removing duplicates
# SKIP

In [79]:

sort(int(uniq))'

Out[79]:

1x5 Array{Int64,2}:
 1  2  4  5  6

PLEAC 4.8: Finding elements in one array but not another¶

In [79]:

a_array = [1,2,4,6,8,10]
b_array = [2,5,6,8,11];

In [80]:

Set(b_array...)

Out[80]:

Set{Int64}(5,6,2,11,8)

In [81]:

setdiff( Set(a_array...), Set(b_array...))

Out[81]:

Set{Int64}(4,10,1)

In [82]:

setdiff(a_array, b_array)'  #arrays get handled automatically; nice!

Out[82]:

1x3 Array{Int64,2}:
 1  4  10

PLEAC 4.9: Computing union, intersection or difference of unique arrays (sets)¶

In [83]:

a = Set(1, 3, 5, 6, 7, 8)
b = Set(2, 3, 5, 7, 9)

Out[83]:

Set{Int64}(5,7,2,9,3)

In [84]:

union(a,b)

Out[84]:

Set{Int64}(5,6,7,2,9,8,3,1)

In [85]:

intersect(a,b)

Out[85]:

Set{Int64}(5,7,3)

In [86]:

symdiff(a,b)

Out[86]:

Set{Int64}(6,2,9,8,1)

PLEAC 4.10: Appending one array to another¶

In [87]:

push!(ar,9)'

Out[87]:

1x8 Array{Int64,2}:
 1  2  2  4  5  6  6  9

In [88]:

append!(ar,[3,4])'

Out[88]:

1x10 Array{Int64,2}:
 1  2  2  4  5  6  6  9  3  4

In [89]:

members = ["Time", "Flies"]
initiates = ["An", "Arrow"]

Out[89]:

2-element Array{ASCIIString,1}:
 "An"   
 "Arrow"

In [90]:

append!(members,initiates)'

Out[90]:

1x4 Array{ASCIIString,2}:
 "Time"  "Flies"  "An"  "Arrow"

In [91]:

insert!(members,3,"Like")'

Out[91]:

1x5 Array{ASCIIString,2}:
 "Time"  "Flies"  "Like"  "An"  "Arrow"

In [92]:

members[1]="Fruit"
members[4:5]=["A","Banana"]
members'

Out[92]:

1x5 Array{ASCIIString,2}:
 "Fruit"  "Flies"  "Like"  "A"  "Banana"

PLEAC 4.11: Reversing an array¶

In [93]:

reverse!(members)'

Out[93]:

1x5 Array{ASCIIString,2}:
 "Banana"  "A"  "Like"  "Flies"  "Fruit"

PLEAC 4.12: Processing multiple elements of an array¶

In [94]:

ar = [i for i in 1:8]
# remove n elements from front of mylist, saving them into fron
front = splice!(ar,1:3)
front'

Out[94]:

1x3 Array{Int64,2}:
 1  2  3

In [95]:

ar'

Out[95]:

1x5 Array{Int64,2}:
 4  5  6  7  8

In [96]:

# remove 1 element from the front , saving it in front
front = splice!(ar,1) 

Out[96]:

In [97]:

ar'

Out[97]:

1x4 Array{Int64,2}:
 5  6  7  8

In [98]:

# remove n elements from the end
splice!(ar,endof(ar)-1:endof(ar))'
ar

Out[98]:

2-element Array{Int64,1}:
 5
 6

In [99]:

# remove n elements from the end, saving them in end
myend = splice!(ar,endof(ar)-1:endof(ar))'

Out[99]:

1x2 Array{Int64,2}:
 5  6

In [100]:

ar = [i for i in 1:8]
myend=pop!(ar)

Out[100]:

In [101]:

function shift2(ar)
    front = splice!(ar,1:2)
    return front
end

Out[101]:

shift2 (generic function with 1 method)

In [102]:

friends = split("Peter Paul Mary Jim Tim")
this, that = shift2(friends)

Out[102]:

2-element Array{String,1}:
 "Peter"
 "Paul"

In [103]:

this, that, friends

Out[103]:

("Peter","Paul",["Mary","Jim","Tim"])

In [104]:

function pop2(ar)
  back = splice!(ar,endof(ar)-1:endof(ar))
end

Out[104]:

pop2 (generic function with 1 method)

In [105]:

beverages = split( "Dew Jolt Cola Sprite Fresca")
pair = pop2(beverages)

Out[105]:

2-element Array{String,1}:
 "Sprite"
 "Fresca"

PLEAC 4.13: Finding the First Array Element That Passes a Test¶

In [106]:

ar'

Out[106]:

1x7 Array{Int64,2}:
 1  2  3  4  5  6  7

In [107]:

criterion(n) = return (n>2) #short form function declaration
criterion(2)

Out[107]:

false

In [108]:

filter( n -> (n>2), ar)'

Out[108]:

1x5 Array{Int64,2}:
 3  4  5  6  7

In [109]:

employees = [("eng",54,"joe"),("law",65,"billy"),("eng",72,"bob")]

Out[109]:

3-element Array{(ASCIIString,Int64,ASCIIString),1}:
 ("eng",54,"joe")  
 ("law",65,"billy")
 ("eng",72,"bob")

In [110]:

#use an anonymous function
eng =filter( emp->(emp[1]=="eng"), employees)

Out[110]:

2-element Array{(ASCIIString,Int64,ASCIIString),1}:
 ("eng",54,"joe")
 ("eng",72,"bob")

In [111]:

sal, idx =findmax([e[2] for e in eng])

Out[111]:

(72,2)

In [112]:

println("Highest paid engineer is: $(eng[idx][3])")

Highest paid engineer is: bob

PLEAC 4.14: Finding All Elements in an Array Matching Certain Criteria¶

In [113]:

matching = filter( emp->(emp[1]=="eng"), employees)

Out[113]:

2-element Array{(ASCIIString,Int64,ASCIIString),1}:
 ("eng",54,"joe")
 ("eng",72,"bob")

In [114]:

nums=999997:1000005
bigs = filter( n -> n>1000000, nums)'

Out[114]:

1x5 Array{Int64,2}:
 1000001  1000002  1000003  1000004  1000005

In [115]:

#SKIP pigs : as it is for Dicts
#SKIP os.popen("who") 

In [116]:

type Empl
    category::String
    salary::Int64
    name::String
end

In [117]:

e1=Empl("eng",45,"Kyle")

Out[117]:

Empl("eng",45,"Kyle")

In [118]:

ear =[ Empl("eng",47,"Jo"), Empl("cat",45,"Kyle"), Empl("eng",56,"Jim")]

Out[118]:

3-element Array{Empl,1}:
 Empl("eng",47,"Jo")  
 Empl("cat",45,"Kyle")
 Empl("eng",56,"Jim")

In [119]:

eng = filter( e-> e.category=="eng", ear)

Out[119]:

2-element Array{Empl,1}:
 Empl("eng",47,"Jo") 
 Empl("eng",56,"Jim")

In [120]:

type Appl
  name::String
  income::Int64
end

In [121]:

appls = [ Appl("Biff",6), Appl("Buff",6), Appl("Boff",6)]

Out[121]:

3-element Array{Appl,1}:
 Appl("Biff",6)
 Appl("Buff",6)
 Appl("Boff",6)

In [122]:

secondary_assistance = filter( appl-> appl.income<30000, appls)

Out[122]:

3-element Array{Appl,1}:
 Appl("Biff",6)
 Appl("Buff",6)
 Appl("Boff",6)

PLEAC 4.16: Sorting an Array Numerically¶

In [123]:

narr = [1,5,3,6,8,3,2]
narr'

Out[123]:

1x7 Array{Int64,2}:
 1  5  3  6  8  3  2

In [124]:

sort(narr)'

Out[124]:

1x7 Array{Int64,2}:
 1  2  3  3  5  6  8

In [125]:

reverse(sort(narr))'

Out[125]:

1x7 Array{Int64,2}:
 8  6  5  3  3  2  1

In [126]:

sort(narr, rev=true)'

Out[126]:

1x7 Array{Int64,2}:
 8  6  5  3  3  2  1

PLEAC 4.17: Sorting an array by a computable field¶

In [127]:

ordered = sort(narr)'

Out[127]:

1x7 Array{Int64,2}:
 1  2  3  3  5  6  8

In [128]:

# computed field for ordering via by fn
ordered = sort(narr, by=(x-> -1x))' 

Out[128]:

1x7 Array{Int64,2}:
 8  6  5  3  3  2  1

In [129]:

# skip sort of /etc/passwd

In [ ]:

PLEAC 4.18: Implementing a circular array¶

In [130]:

# there has to be a better way to do this
type Circlei
  index::Int64
end

Circlei() = Circlei(1)

Out[130]:

Circlei (constructor with 2 methods)

In [131]:

circ = Circlei()

Out[131]:

Circlei(1)

In [132]:

import Base.next
function next(c::Circlei)
    c.index = ((c.index+1) % 5)
    c.index = c.index==0 ? 5 : c.index
end

Out[132]:

next (generic function with 45 methods)

In [133]:

next(circ)

Out[133]:

In [134]:

abort_counter = 0
while abort_counter<7
    next(circ)
    println("Handling process $(circ.index)")
    abort_counter+=1
end

Handling process 3
Handling process 4
Handling process 5
Handling process 1
Handling process 2
Handling process 3
Handling process 4

PLEAC 4.19: Randomizing an array¶

In [135]:

ar'

Out[135]:

1x7 Array{Int64,2}:
 1  2  3  4  5  6  7

In [136]:

shuffle(ar)'

Out[136]:

1x7 Array{Int64,2}:
 1  2  4  6  3  5  7

In [137]:

shuffle!(ar) #in place
ar'

Out[137]:

1x7 Array{Int64,2}:
 7  6  1  4  3  5  2

PLEAC 4.20: Program words¶

SKIP

PLEAC 4.21: Program permute¶

SKIP

In [140]:

;ipython nbconvert 4_pleac_arrays.ipynb

[NbConvertApp] Using existing profile dir: u'C:\\Users\\keithc\\.ipython\\profile_default'
[NbConvertApp] Converting notebook 4_pleac_arrays.ipynb to html
[NbConvertApp] Support files will be in 4_pleac_arrays_files\
[NbConvertApp] Loaded template html_full.tpl
[NbConvertApp] Writing 334838 bytes to 4_pleac_arrays.html

In [139]: