import matplotlib.pyplot as plt

import cartopy
import cartopy.crs as ccrs
import iris
import iris.coord_categorisation as coord_cat

print('Iris version: {}'.format(iris.__version__))
print('Cartopy version: {}'.format(cartopy.__version__))

a1b_cube = iris.load_cube(iris.sample_data_path('A1B_north_america.nc'))
print a1b_cube

coord_cat.add_year(a1b_cube, 'time')
after_1980 = a1b_cube.extract(iris.Constraint(year=lambda cell: cell>1979))
print after_1980

def decade_from_time(coord, point):
    years = coord.units.num2date(point).year
    return (years/10) * 10

coord_cat.add_categorised_coord(after_1980, 'decade', 'time', decade_from_time)
print after_1980

decadal_means = after_1980.aggregated_by('decade', iris.analysis.MEAN)
print decadal_means

print decadal_means.coord('time')

import iris.quickplot as qplt
qplt.plot(after_1980[:, 0, 0])
qplt.plot(decadal_means[:, 0, 0], drawstyle='steps-mid')
qplt.show()