Parse every column of a .csv file into a single list python

Question

I have a following type of csv

a,b,c
1,2,3
4,5,6
7,8,9

I would like to parse every column of this csv file into a list with out columns so the end result would be

myList = ["1","4","7","2","5","8","3","6","9"]

I have found many solutions for one column but i need to be flexible to be able to read every column of the file. I'm using an older version of python so i can't use any solutions with pandas library.

There is no direct way to do this, you have to loop through each row and add that in single `array` — Nilesh, May 10 '17 at 18:42

Jean-François Fabre · Answer 1 · 2017-05-10T19:22:51.073

5

You could read the file fully and then zip the rows to transpose them, then chain the result to flatten the list. Standalone example (using a list of strings as input):

import csv,itertools

text="""a,b,c
1,2,3
4,5,6
7,8,9
""".splitlines()

myList = list(itertools.chain.from_iterable(zip(*csv.reader(text[1:]))))

print(myList)

result:

['1', '4', '7', '2', '5', '8', '3', '6', '9']

from a file it would read:

with open("test.csv") as f:
    cr = csv.reader(f,separator=",")  # comma is by default, but just in case...
    next(cr)  # skip title
    myList = list(itertools.chain.from_iterable(zip(*cr)))

edited May 10 '17 at 19:22

answered May 10 '17 at 18:46

Jean-François Fabre

137,073
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splitlines() was just to create a standalone example. you don't need splitlines for a file. Check my second example where the input is a file. Don't use a `DictReader` because the order of the values would depend on the order of the keys, which isn't what you want. – Jean-François Fabre May 10 '17 at 19:12
Thanks, I tried the code, but i get ['1;2;3', '4;5;6', '7;8;9'], nvm ... excel was screwing me over ... it added a ';' instead of ',' – stewazy May 10 '17 at 19:21
that's because your file doesn't match the file you posted. Try adding a separator (see my edit) – Jean-François Fabre May 10 '17 at 19:22

score 0 · Answer 2 · answered May 10 '17 at 18:49

Simple approach:

d = """a,b,c
1,2,3
4,5,6
7,8,9
"""

cells = []
for line in d.split("\n"):
    if line:
        cells.append(line.strip().split(','))

print(cells)

for n in range(len(cells[0])):
    for r in cells:
        print(r[n])

Same iteration, but as generator:

def mix(t):
    for n in range(len(t[0])):
        for r in t:
            yield r[n]

print( list( mix(cells) )  )

score 0 · Answer 3 · answered May 10 '17 at 18:50

Using csv and chain to flatten the list

import csv
from itertools import chain

l = list(csv.reader(open('text.csv', 'r')))
mylist = map(list, zip(*l[1:])) # transpose list
list(chain.from_iterable(mylist)) # output ['1', '4', '7', '2', '5', '8', '3', '6', '9']

Parse every column of a .csv file into a single list python

3 Answers3