Passing multiple arguments to apply (Python)

Question

I'm trying to clean up some code in Python to vectorize a set of features and I'm wondering if there's a good way to use apply to pass multiple arguments. Consider the following (current version):

def function_1(x):
    if "string" in x:
        return 1
    else:
        return 0

df['newFeature'] = df['oldFeature'].apply(function_1)

With the above I'm having to write a new function (function_1, function_2, etc) to test for each substring "string" that I want to find. In an ideal world I could combine all of these redundant functions and use something like this:

def function(x, string):
    if string in x:
        return 1
    else:
        return 0

df['newFeature'] = df['existingFeature'].apply(function("string"))

But trying that returns the error TypeError: function() takes exactly 2 arguments (1 given) Is there another way to accomplish the same thing?

Edit:

def function(string, x):
    if string in x:
        return 1
    else:
        return 0

df['newFeature'] = df['oldFeature'].apply(partial(function, 'string'))

Roman Bodnarchuk · Accepted Answer · 2013-10-02 15:01:47Z

14

I believe you want functools.partial. A demo:

>>> from functools import partial
>>> def mult(a, b):
...     return a * b
...
>>> doubler = partial(mult, 2)
>>> doubler(4)
8

In your case you need to swap arguments in function (because of idea of partial), and then just

df['existingFeature'].apply(partial(function, "string"))

answered Oct 2, 2013 at 15:01

Roman Bodnarchuk

29.8k12 gold badges62 silver badges76 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Bakuriu Over a year ago

Or he could simply use a lambda: doubler = lambda b: mult(b, 2). With a lambda you can fix whatever values you want, while partial can only fix positional arguments as they are specified.

chepner Over a year ago

In many cases, you can specify keyword arguments: partial(mult, a=5) or partial(mult, b=5). (This does require you to know the names of the arguments, which may not be documented.)

Collectives™ on Stack Overflow

Passing multiple arguments to apply (Python)

Edit:

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

Edit:

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related