Python Language Map Function Mapping values of different iterables
Example
For example calculating the average of each i-th element of multiple iterables:
def average(*args):
return float(sum(args)) / len(args) # cast to float - only mandatory for python 2.x
measurement1 = [100, 111, 99, 97]
measurement2 = [102, 117, 91, 102]
measurement3 = [104, 102, 95, 101]
list(map(average, measurement1, measurement2, measurement3))
# Out: [102.0, 110.0, 95.0, 100.0]
There are different requirements if more than one iterable is passed to map depending on the version of python:
-
The function must take as many parameters as there are iterables:
def median_of_three(a, b, c): return sorted((a, b, c))[1] list(map(median_of_three, measurement1, measurement2))TypeError: median_of_three() missing 1 required positional argument: 'c'
list(map(median_of_three, measurement1, measurement2, measurement3, measurement3))TypeError: median_of_three() takes 3 positional arguments but 4 were given
Python 2.x2.0.1
-
map: The mapping iterates as long as one iterable is still not fully consumed but assumesNonefrom the fully consumed iterables:import operator measurement1 = [100, 111, 99, 97] measurement2 = [102, 117] # Calculate difference between elements list(map(operator.sub, measurement1, measurement2))TypeError: unsupported operand type(s) for -: 'int' and 'NoneType'
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itertools.imapandfuture_builtins.map: The mapping stops as soon as one iterable stops:import operator from itertools import imap measurement1 = [100, 111, 99, 97] measurement2 = [102, 117] # Calculate difference between elements list(imap(operator.sub, measurement1, measurement2)) # Out: [-2, -6] list(imap(operator.sub, measurement2, measurement1)) # Out: [2, 6]
Python 3.x3.0.0
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The mapping stops as soon as one iterable stops:
import operator measurement1 = [100, 111, 99, 97] measurement2 = [102, 117] # Calculate difference between elements list(map(operator.sub, measurement1, measurement2)) # Out: [-2, -6] list(map(operator.sub, measurement2, measurement1)) # Out: [2, 6]
