CODEWITHSUNDEEP
pythonlistsorting
d.b
d.b

Reputation: 32558

Order a list based on two different lists

What is the proper way to order elements in one list based on values of two (or more lists) in base Python. Say I have three lists:

X = ["a", "b", "c", "d", "e", "f", "g", "h", "i"]
Y = [0, 1, 1, 0, 1, 2, 2, 0, 1]
Z = [2, 1, 2, 1, 2, 1, 2, 1, 1]

I want to order the values of X first based on Z and then based on Y. The desired output would be:

["d", "h", "b", "i", "f", "a", "c", "e", "g"]

Upvotes: 0

Views: 53

Answers (1)

MSeifert
MSeifert

Reputation: 152860

You could simply zip the lists and then use sorted plus unpacking:

>>> [i[2] for i in sorted(zip(Z, Y, X))]
['d', 'h', 'b', 'i', 'f', 'a', 'c', 'e', 'g']

By zipping it with Z first and Y as second input it will give the desired order - and the outer comprehension discards the Z and Y again leaving you with the X values. Okay, in case both Z and Y are equal it will breaks ties by comparing the X (which could be undesired according to the question), you could disable that by using a custom key function that excludes X:

>>> [i[2] for i in sorted(zip(Z, Y, X), key=lambda x: (x[0], x[1]))]
['d', 'h', 'b', 'i', 'f', 'a', 'c', 'e', 'g']

Upvotes: 4

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