Efficiently unpack CSV columns into separate lists

Question

I am optimizing my script and find this problem:

Here I have a csv file where the first column is just index and the second column contains a string (sentence of arbitrary length). I want to create two variables "index" and "string" that contains all the index and string respectively. This is my code:

with open(file_name, 'r', encoding="utf8") as csvfile:
    train_set_x = csv.reader(csvfile, delimiter=',', quotechar='|')
    index = [[c[0],c[1]] for c in train_set_x]
    text = [a[1] for a in index]

this does the job, however, it takes 2 iterations. I am asking if there is a cleaner way to do it? Thank you

cs95 · Accepted Answer · 2017-10-15T23:39:57.767

1

There definitely is. Use zip with iterable unpacking.

index, text = zip(*((c[0], c[1]) for c in train_set_x))

MCVE:

In [152]: x, y = zip(*[(1, 2), (3, 4), (5, 6)])

In [153]: x
Out[153]: (1, 3, 5)

In [154]: y
Out[154]: (2, 4, 6)

edited Oct 15 '17 at 23:39

answered Oct 15 '17 at 23:35

cs95

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Thank you. This answer will be adopted. I can't do it in another 11 mins – Yi Shen Oct 15 '17 at 23:36
@YiShen Do mean "accepted" ? :D :D *Adopted* sounds better though. SO should change it in the documentation – Moinuddin Quadri Oct 15 '17 at 23:40

Efficiently unpack CSV columns into separate lists

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