Transposes the contents of a CSV file and writes the CSV result to another file.

csv-transposer

#! /usr/bin/env python

"""CSV transposer

Transposes the contents of a CSV file and writes the CSV result to another
file.
(see: http://en.wikipedia.org/wiki/Transpose)

Runs on Python 2.7.3

"""

import unittest

def parse_csv(csv):
    rows = csv.split("\n")

    # assume that columns and rows are even
    num_rows = len(rows)
    num_columns = rows[0].count(",") + 1

    matrix = []

    for i in range(num_rows):
        matrix.append(rows[i].split(","))
    
    return matrix

def transpose(matrix):
    # assume that columns and rows are even
    num_rows = len(matrix)
    num_columns = len(matrix[0])

    transposed_matrix = []

    for x in range(num_rows):
        for y in range(num_columns):
            if (x == 0): # only once for each row
                transposed_matrix.append([])
            transposed_matrix[y].append(matrix[x][y])
    
    return transposed_matrix

def matrix_to_csv(matrix):
    # assume that columns and rows are even
    num_rows = len(matrix)
    num_columns = len(matrix[0])

    csv = ""
    # str.join() only accepts 1 parameter in 2.7.3
    # 2.7.6 - str.join(sequence [,sep])
    for x in range(num_rows):
        for y in range(num_columns):
            csv = csv + matrix[x][y]
            if (y < num_columns - 1):
                csv = csv + ","
        if (x < num_rows - 1):
            csv = csv + "\n"
    
    return csv

class TransposerTests(unittest.TestCase):
    def test_parse_csv(self):
        csv = """1,2,3
4,5,6
7,8,9
10,11,12"""
        matrix = [['1','2','3'],
                 ['4','5','6'],
                 ['7','8','9'],
                 ['10','11','12']]
        self.assertEquals(parse_csv(csv), matrix)

    def test_transpose(self):
        matrix1 = [[1,2,3],
                  [4,5,6],
                  [7,8,9],
                  [10,11,12]]
        matrix2 = [[1,4,7,10],
                  [2,5,8,11],
                  [3,6,9,12]]
        self.assertEquals(transpose(matrix1), matrix2)

    def test_matrix_to_csv(self):
        matrix = [['1','4','7','10'],
                  ['2','5','8','11'],
                  ['3','6','9','12']]
        csv = """1,4,7,10
2,5,8,11
3,6,9,12"""
        self.assertEquals(matrix_to_csv(matrix), csv)

if __name__ == '__main__':
    # unittest exits upon completion; code after the call won't be executed
    # unittest.main()
    
    filename = raw_input("Source file: ")
    orig_text = ""
    with open(filename, "rb") as p:
        orig_text = str.strip(p.read())
    transposed_text = matrix_to_csv(transpose(parse_csv(orig_text)))

    split_filename = filename.split(".")
    transposed_filename = split_filename[0] + "-transposed." + split_filename[1]
    with open(transposed_filename, "wb") as t:
        t.write(transposed_text)