CSV into list in Python

Question

I have imported a .csv file into Python and named it data. It looks something like this:

aK    bK    id
.124  .121  1
.320  .202  2
.222  .198  3

And so on for a few hundred rows. How do I convert column aK and column bK into lists? I have tried this:

aK = []
for row in data:
    aK.append(row[0])

But aK is still a blank list.

@japem I think he's asking how you loaded the file and converted it to a python string/list/other object. Were you using the csv module? — senshin
– senshin, Commented Dec 24, 2014 at 16:45
Oh. Yes I was. >>> Import csv >>> a = open('MyFile.csv') >>> data = csv.reader(a) — japem
– japem, Commented Dec 24, 2014 at 16:46
@japem For the code you've posted in comment it's hard to belive aK is empty after the loop, post the actual code in question body.(Perhaps you consumed the file object before you passed it to csv.reader) — Ashwini Chaudhary
– Ashwini Chaudhary, Commented Dec 24, 2014 at 16:50

Hugh Bothwell · Accepted Answer · 2014-12-24 16:55:57Z

3

import csv

CSV_FILE = "test.csv"

def main():
    with open(CSV_FILE) as inf:
        in_csv = csv.reader(inf, delimiter=" ", skipinitialspace=True)
        header = next(in_csv)       # skip header row
        ak, bk, id = zip(*in_csv)   # get columns

if __name__ == "__main__":
    main()

which gives

ak = ('.124', '.320', '.222')
bk = ('.121', '.202', '.198')
id = ('1', '2', '3')

edited Dec 24, 2014 at 16:55

answered Dec 24, 2014 at 16:45

Hugh Bothwell

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4 Comments

japem Over a year ago

Is the "test.csv" file the one I originally imported?

user2555451 Over a year ago

@Hackaholic - Why reinvent the wheel? Importing a module is trivial in Python. Besides, the csv module will be more robust than anything handcrafted.

Hackaholic Over a year ago

@iCodez this 4 line of code, i dont think reinvent the whell, and all this csv module make use of this built function like split and strip only

jamylak Over a year ago

@HughBothwell I can see why you looked for delimiter=" " skipping initial spaces. That makes sense for the data on this website but I think it's very likely OP had used a tab delimited file and Stackoverflow converted them to spaces or the text editor did

jamylak · Accepted Answer · 2014-12-25 06:20:14Z

0

The way you approached it seems fine. You just didn't show how you created data

>>> import csv
>>> with open('data.csv') as f:
        aK, bK = [], []
        next(f) # skip headers
        for row in csv.reader(f, delimiter='\t'):
            aK.append(float(row[0]))
            bK.append(float(row[1]))


'aK\tbK\tid\n'
>>> aK
[0.124, 0.32, 0.222]
>>> bK
[0.121, 0.202, 0.198]

answered Dec 25, 2014 at 6:20

jamylak

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