python - Replacing elements in a list with the indices of a list containing all unique elements -

assume have list contains unique nodes a-d of graph:

list1 = [a, b, c, d]

and list, contains edges of graph pairs of elements:

list2 = [[c, d], [b, a], [d, a], [c, b]]

how can write fast , economic way replace elements of list2 indices of elements in list1, get:

list3 = [(2, 3), (1, 0), (3, 0), (2, 1)]

my current way of doing is:

for in range(len(list2)):     list3[i] = (list1.index(list2[i][0]), list1.index(list2[i][1]))

however, takes long time large list, , trying find potentially faster way this.

you can create dict letters indices want

>>> indices = {key: index index, key in enumerate(list1)} >>> indices {'b': 1, 'd': 3, 'a': 0, 'c': 2}

then use nested list comprehension

>>> [[indices[i] in sub] sub in list2] [[2, 3], [1, 0], [3, 0], [2, 1]]

edit
list of tuple

>>> [tuple(indices[i] in sub) sub in list2] [(2, 3), (1, 0), (3, 0), (2, 1)]

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