How can I get an index of an outer list element in a list of lists?

Question

I have a list:

mylist = [[0, [0]], [2, [1]], [3, [4]], [4, [1, 4]]]

I want to get the index of the element of the outer list given the element.

I have tried this, but this only fetches me the outer elements of the list.

get_index = [outer for outer, inner in mylist]

I want something like this:

Input: 2
Output: 1

Input: 4
Output: 3

Possible duplicate of [Finding the index of elements based on a condition using python list comprehension](https://stackoverflow.com/questions/7270321/finding-the-index-of-elements-based-on-a-condition-using-python-list-comprehensi) — mkrieger1, May 21 '19 at 14:38

score 3 · Accepted Answer · answered May 21 '19 at 14:34

3

You could use a dictionary comprehension with enumerate to easily look up the index from the first values:

d = {i[0]:ix for ix, i in enumerate(mylist)}
# {0: 0, 2: 1, 3: 2, 4: 3}

d[2]
# 1

d[4]
# 3

answered May 21 '19 at 14:34

yatu

80,714
11
64
111

1

Thank you! That did it! – AlyssaAlex May 22 '19 at 07:45

score 0 · Answer 2 · answered May 21 '19 at 14:37

0

A function matching the desired input/output behavior:

def loc( x, ml ):
    return [a for a,b in ml].index(x)

answered May 21 '19 at 14:37

Scott Hunter

46,905
10
55
92

score 0 · Answer 3 · answered Jun 01 '19 at 21:32

0

You can also create a function to which you pass an Input and get the corresponding index as output

def get_index(inp):
    idx = [i for i, j in enumerate(mylist) if inp==j[0]]
    return idx[0]

inp = 2
get_index(inp)
# 1

inp = 4
get_index(inp)
# 3

answered Jun 01 '19 at 21:32

Sheldore

35,129
6
43
58

How can I get an index of an outer list element in a list of lists?

3 Answers3