How to get the index comparing two lists of different lengths in Python?

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How to get the index comparing two lists of different lengths in Python?

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#1 by (2 votes)

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I have two different lists in two CSV files.

The first list has 47843 items and the second 813331, which is the first multiplied by 17.

I want to get the index position in the first, based on the value of the second, because the second one repeats the value and does not have the same order as this:

Fisrt
1:   ARS-BFGL-BAC-10919
2:   ARS-BFGL-BAC-10975
3:   ARS-BFGL-BAC-11000
4:   ARS-BFGL-BAC-11003
5:   ARS-BFGL-BAC-11025
6:   ARS-BFGL-BAC-11044
7:   ARS-BFGL-BAC-11193
8:   ARS-BFGL-BAC-11215
9:   ARS-BFGL-BAC-11218
10:  ARS-BFGL-BAC-11276

Second:

1:    ARS-BFGL-BAC-10919
2:    ARS-BFGL-BAC-11003
3:    ARS-BFGL-BAC-10975
4:    ARS-BFGL-BAC-11044
5:    ARS-BFGL-BAC-11000
6:    ARS-BFGL-BAC-10975
7:    ARS-BFGL-BAC-11025
8     ARS-BFGL-BAC-11193
9:    ARS-BFGL-BAC-11044
.
.
.
.
.
.

I want this result:

{1,4,2,6,3,2,5,7,6....}

python lista order

asked by anonymous 06.09.2018 / 21:14

1 answer

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score 2 · Accepted Answer

Since you did not provide any code, I'll make it up here in a simple way:

lista1 = [
    'ARS-BFGL-BAC-10919',
    'ARS-BFGL-BAC-10975',
    'ARS-BFGL-BAC-11000',
    'ARS-BFGL-BAC-11003',
    'ARS-BFGL-BAC-11025',
    'ARS-BFGL-BAC-11044',
    'ARS-BFGL-BAC-11193',
    'ARS-BFGL-BAC-11215',
    'ARS-BFGL-BAC-11218',
    'ARS-BFGL-BAC-11276',
]
lista2 = [
    'ARS-BFGL-BAC-10919',
    'ARS-BFGL-BAC-11003',
    'ARS-BFGL-BAC-10975',
    'ARS-BFGL-BAC-11044',
    'ARS-BFGL-BAC-11000',
    'ARS-BFGL-BAC-10975',
    'ARS-BFGL-BAC-11025',
    'ARS-BFGL-BAC-11193',
    'ARS-BFGL-BAC-11044',
]

The simplest solution uses normal indexing, it can be slow because it will search each element of a list in the other:

>>> print(tuple(lista1.index(elem)+1 for elem in lista2))
(1, 4, 2, 6, 3, 2, 5, 7, 6)

Another solution is to convert list1 to dictionary - dictionary search is almost instant so it would be much faster:

>>> d1 = {item: index for index, item in enumerate(lista1, start=1)}
>>> print(tuple(d1.get(elem) for elem in lista2)
(1, 4, 2, 6, 3, 2, 5, 7, 6)