picking and writing out some fractions of list with for-loop

Question

There is a dataset as a csv-file which contains some tabular of data.
I want to pick out the fractions with the same number.
For example i have one list

a = [1,1,2,2,3,3,4,4,4,5,5,5,5,6]

and i want a loop, which writes text-files with the same numbers
file_1.txt contains 1,1
file_2.txt contains 2,2
file_3.txt contains 3,3
file_4.txt contains 4,4,4
file_5.txt contains 5,5,5,5
file_6.txt contains 6

I still have no real result, because so far everything is wrong.

Even if your result is wrong and does not seem to work, please share with us your attempt. — offeltoffel, Jan 07 '19 at 12:45
do you expect the output to repeat the same number n times? Or do you just want to get the count for each element? — Felk, Jan 07 '19 at 12:49
@Felk: The desired output seems to be clear here if you look at `a`. The point is his/her attempt — Sheldore, Jan 07 '19 at 12:57

score 0 · Answer 1 · answered Jan 07 '19 at 13:10

0

If I understood correctly, this should work:

for x in set(a):
    text_file = open("file_"+str(x)+".txt", "w")
    text_file.write(((str(x)+',')*a.count(x))[:-1])
    text_file.close()

Where that [:-1] in the third line is to remove extra comma ;)

answered Jan 07 '19 at 13:10

Ala Tarighati

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pault · Accepted Answer · 2019-01-08T16:06:52.967

A much cleaner approach would be to use itertools.groupby and str.join:

from itertools import groupby

for num, group in groupby(a):
    filename = "file_%d.txt"%num
    with open(filename, 'w') as f:
        f.write(",".join(map(str, group)) + "\n")

Another important point is that you should always use the with statement when reading and writing to files.

Using groupby assumes that the data is already sorted. Another approach would be to use collections.Counter:

from collections import Counter

for num, count in Counter(a).items():
    filename = "file_%d.txt"%num
    with open(filename, 'w') as f:
        f.write(",".join([str(num)]*count) + "\n")

picking and writing out some fractions of list with for-loop

2 Answers2