CODEWITHSUNDEEP
pythonvectorization
Thomas Leyshon
Thomas Leyshon

Reputation: 107

Cleanest way to apply a function with multiple variables to a list using map()?

I have a function which has more than one input variable. For a particular case only one of the input variables is being varied, is it possible to apply this function using a map without having to make a list of the non-varying variables?

For example:

# Example multiple variable input function
def Example_Function(x,y):
    return x**2+y**2

# Example List changing variable, x
List_of_x = [x for x in range(0,100)]

# Non-varying y
y = 4

# The naive version of the application (doesn't work)
Naive_Result_of_map_application = list(map(Example_Function, List_of_x, [y]))

# The result we want where we have to make a list of y ([y for i in range(0,100)])
Result_of_map_application = list(map(Example_Function, List_of_x, [y for i in range(0,100)]))

So, is there a way to get Result_of_map_application without having to do [y for i in range(0,100)]?

Upvotes: 0

Views: 654

Answers (3)

ShadowRanger
ShadowRanger

Reputation: 155418

Answering your question as asked:

You can just use itertools.repeat(y) to make an iterator that produces y forever (map will stop when the other iterator is exhausted). If it must stop after a certain number of repetitions, you can pass the count as a second parameter, e.g. itertools.repeat(y, 100).

This would make your code:

from itertools import repeat  # At top of file

Result_of_map_application = list(map(Example_Function, List_of_x, repeat(y)))

That said, in this circumstance, I'd personally recommend the more readable listcomp provided by Carcigenicate.

Upvotes: 2

Carcigenicate
Carcigenicate

Reputation: 45750

I'd personally do away with map. If you don't want y to change, I just wouldn't put it in a context that expects changing data. A list comprehension works fine here:

Result_of_map_application = [Example_Function(x, y) for x in List_of_x]

Upvotes: 4

Dani Mesejo
Dani Mesejo

Reputation: 61910

Create a new function that already sets the y parameter:

# Example multiple variable input function 
def example_function(x, y):
    return x ** 2 + y ** 2


# Example List changing variable, x
list_of_x = [x for x in range(0, 100)]

# Non-varying y
y = 4

new_example_function = lambda x : example_function(x, y)

# The result we want where we have to make a list of y ([y for i in range(0,100)])
Result_of_map_application = list(map(new_example_function, list_of_x))

As an alternative make them optional, and use partial:

from functools import partial


def example_function(x=1, y=4):
    return x ** 2 + y ** 2


list_of_x = [x for x in range(0, 100)]
y = 4

new_example_function = partial(example_function, y=4)
result_of_map_application = list(map(new_example_function, list_of_x))

Upvotes: 2

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