Question

lambda
map
filter
reduce
fold
concat
flatmap
aggregate
groupby

from __future__ import division
import os
import sys
import glob
import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
%matplotlib inline
%precision 4
plt.style.use('ggplot')

! pip install toolz

Requirement already satisfied (use --upgrade to upgrade): toolz in /Users/cliburn/anaconda/lib/python2.7/site-packages

from toolz import countby, groupby, accumulate, reduce, compose, partition
from operator import add, itemgetter

Anonymous functions, map and filter

x = range(10)
map(lambda x: x*x, filter(lambda x: x%2==0, x))

[0, 4, 16, 36, 64]

Reduce, accumulate and fold

reduce(add, x, 0)

45

Flatmap and function composition

flatmap = compose(concat, map)

from string import split

s = ["hello world", "this is the end"]
print list(map(split, s))
print list(flatmap(split, s))

[['hello', 'world'], ['this', 'is', 'the', 'end']]
['hello', 'world', 'this', 'is', 'the', 'end']

Working with key-value pairs

s = 'aabaabcdeda'
a = [(_, 1) for _ in s]
print a

[('a', 1), ('a', 1), ('b', 1), ('a', 1), ('a', 1), ('b', 1), ('c', 1), ('d', 1), ('e', 1), ('d', 1), ('a', 1)]

[item[0] for item in g.itervalues()]

[('a', 1), ('c', 1), ('b', 1), ('e', 1), ('d', 1)]

groupby(itemgetter(0), a, )

{'a': [('a', 1), ('a', 1), ('a', 1), ('a', 1), ('a', 1)],
 'b': [('b', 1), ('b', 1)],
 'c': [('c', 1)],
 'd': [('d', 1), ('d', 1)],
 'e': [('e', 1)]}

countby(itemgetter(0), a)

{'a': 5, 'b': 2, 'c': 1, 'd': 2, 'e': 1}