Apply Function to Elements Over a List

Apply function to each element of a list

Using the built-in standard library map:

>>> mylis = ['this is test', 'another test']
>>> list(map(str.upper, mylis))
['THIS IS TEST', 'ANOTHER TEST']

In Python 2.x, map constructed the desired new list by applying a given function to every element in a list.

In Python 3.x, map constructs an iterator instead of a list, so the call to list is necessary. If you are using Python 3.x and require a list the list comprehension approach would be better suited.

Apply function to all items in a list Python

You can use map approach:

list(map(myCoolFunction, my_list))

This applies defined function on each value of my_list and creates a map object (3.x). Calling a list() on it creates a new list.

Apply function to all the elements (lists of strings) of a column to convert into floats

I think the error is due to the presence of NaN values in the column c, one way to fix this is to remove the NaN values before applying the map function:

df['c'] = df['c'].dropna().apply(lambda x: list(map(float, x)))

Apply function to a list of lists

you don't need for loops to do so. You can directly work with lapply:

lapply(dati_fault, \(x) colMeans(do.call(rbind, x)))

This does the following: for each entry of dati_fault (i.e. each sublist of 31 matrices) these matrices are bound together (using rbind) into one single matrix with 310 rows and 5 columns. Then, colMeans is applied to this matrix.

If you are not familiar with the shorthand notation for anonymous functions (i.e. \(x)) you can read about it here.

apply a function over each element of an iterable with sublists

Sounds like recursion should be able to solve that:

a = [1,2,3]
b = [[1,2,3], [4,5,6]]
c = [[[1,2,3], [4,5,6]], [[7,8,9], [10,11,12]]]

f = lambda x : x+1

def apply(iterable, f): 
    # suggestion by Jérôme:
    # from collections.abc import Iterable and use
    # isinstance(iterable, collections.abc.Iterable) so it works for tuples etc. 
    if isinstance(iterable, list):
        # apply function to each element
        return [apply(w, f) for w in iterable]
    else:
        return f(iterable)

print(apply(a, f)) # [2,3,4]
print(apply(b, f)) # [[2,3,4],[5,6,7]]
print(apply(c, f)) # [[[2,3,4],[5,6,7]],[[8,9,10],[11,12,13]]]

How to apply function to elements of a list?

And what's wrong with

for i in my_things:
    i.size = "big"

You don't want to use neither map nor list comprehansion because they actually create new lists. And you don't need that overhead, do you?