filter a list based on values in another list

Question

list1 = ['a','b','c','d']
list2 = [1,0,1,0]

Given two lists like the above, I would like to obtain a third list whose values are ['a','c']

In other words, I'd like the target list to be the values from list1 where the corresponding element in list2 is 1.

HHC · Accepted Answer · 2020-09-08 01:27:14Z

1

As noted in the comments:

[i for i, j in zip(list1, list2) if j] would work.

Alternatively, if you were looking for something not so advanced:

list3 = []

for i in range(len(list1)):
    if list2[i] == 1:
        list3.append(list1[i])

answered Sep 8, 2020 at 1:27

HHC

796 bronze badges

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

Comments

wjandrea · Accepted Answer · 2021-11-13 22:01:09Z

1

Use enumerate function on second list to include index, which can be used for the first list.

[list1[i] for i, item in enumerate(list2) if item]

wjandrea

34k10 gold badges69 silver badges105 bronze badges

answered Sep 8, 2020 at 1:22

pygeek

7,4241 gold badge22 silver badges41 bronze badges

neutrino_logic · Accepted Answer · 2020-09-08 01:37:24Z

0

Generators can be nice if you have very long lists:

def filterfunc(a, b, keyvalue=1):
    return (x for i, x in enumerate(a) if b[i] == keyvalue)

To get the whole sequence:

list(filterfunc(a, b))

answered Sep 8, 2020 at 1:37

neutrino_logic

1,2991 gold badge8 silver badges11 bronze badges