Python CSV transpose data in one column to rows

Question

I have a CSV file containing data only in the first column,

I want to use python to transpose every 4 rows to another empty CSV file, for example, row 1 to row 4 transposed to the first row; then row 5 to row 8 transposed to the second row,...etc, and finally we can get a 5 * 4 matrix in the CSV file.

How to write a script to do this？ Please give me any hint and suggestion, thank you.

I am using python 2.7.4 under Windows 8.1 x64.

---

update#1

I use the following code provided by thefortheye,

import sys, os
os.chdir('C:\Users\Heinz\Desktop')
print os.getcwd()

from itertools import islice
with open("test_csv.csv") as in_f, open("Output.csv", "w") as out_file:
    for line in ([i.rstrip()] + map(str.rstrip, islice(in_f, 3)) for i in in_f):
        out_file.write("\t".join(line) + "\n")

the input CSV file is,

and the result is,

This is not what I want.

Answer 1

You can use List comprehension like this

data = range(20)
print data
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
print[data[i:i + 4] for i in xrange(0, len(data), 4)]
# [[0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11], [12, 13, 14, 15], [16, 17, 18,19]]

Instead of 4, you might want to use 56.

Since you are planing to read from the file, you might want to do something like this

from itertools import islice
with open("Input.txt") as in_file:
    print [[int(line)] + map(int, islice(in_file, 3)) for line in in_file]

Edit As per the updated question,

from itertools import islice
with open("Input.txt") as in_f, open("Output.txt", "w") as out_file:
    for line in ([i.rstrip()] + map(str.rstrip, islice(in_f, 3)) for i in in_f):
        out_file.write("\t".join(line) + "\n")

Edit: Since you are looking for comma separated values, you can join the lines with ,, like this

        out_file.write(",".join(line) + "\n")

Answer 2

You can use List comprehension and double-loop like this.

>>> M = 3
>>> N = 5
>>> a = range(M * N)
>>> o = [[a[i * N + j] for j in xrange(N)] for i in xrange(M)]
>>> print o
[[ 0,  1,  2,  3,  4],
 [ 5,  6,  7,  8,  9],
 [10, 11, 12, 13, 14]]