CODEWITHSUNDEEP
pythonlist
Mathieu
Mathieu

Reputation: 65

Return list of index of two lists given a third list

What is the smartest and most pythonic way to achieve this please:

input:

i1 = [A,A,B]
i2 = [x,y,x]
i3 = [0,1,2]

parameter:

list = [[A,x],[B,x],[A,y]]

(or list = [[A,B,A],[x,z,y]] if easier)

One needs to find the index idx when list matches i1 and i2 and output i3[idx]

output:

output = [0,2,1]

I was thinking about list comprehensions to find all occurences of (element1,element2) in i1 and i2 but I can't manage to do it:

idxs = [i for i,v in enumerate(zip(i1,i2)) if v==(x[0],x[1]) for x in list]

Upvotes: 1

Views: 46

Answers (2)

Adam.Er8
Adam.Er8

Reputation: 13413

Your comprehension was very close,

Here I'm using an almost identical one to create a dictionary mapping a pair to an index, and then just get the indexes from it:

i1 = ['A','A','B']
i2 = ['x','y','x']

d = {tup: idx for idx,tup in enumerate(zip(i1,i2))}

list = [['A','x'],['B','x'],['A','y']]

result = [d[tuple(pair)] for pair in list]

print(result)

Output:

[0, 2, 1]

Upvotes: 3

Horace
Horace

Reputation: 1054

One way of doing this is by using a dictionary:

i1 = ['A','A','B']
i2 = ['x','y','x']
i3 = [0,1,2]
list = [['A','x'],['B','x'],['A','y']]

mapping = dict(zip(zip(i1, i2), i3))
out = [mapping[tuple(e)] for e in list]
print(out)

[0, 2, 1]

Upvotes: 2

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