Question

I am trying to use Python to write to an existing .csv file but instead of appending the data to the bottom of the existing file, I would like to append the new information to a new column of the .csv file. The reason for this is that I am wanting to “infinitely” loop through a read data section of code and then add the data read during each loop iteration to a new column, instead of row. In essence, I would like something as follows:

Row1Iteration1, Row1Iteration2, Row1Iteration3,..., Row1IterationX
Row2Iteration1, Row2Iteration2, Row2Iteration3,..., Row2IterationX
Row3Iteration1, Row3Iteration2, Row3Iteration3,..., Row3IterationX
Row4Iteration1, Row4Iteration2, Row4Iteration3,..., Row4IterationX
Row5Iteration1, Row5Iteration2, Row5Iteration3,..., Row5IterationX

Instead of:

Row1Iteration1
Row2Iteration1
Row3Iteration1
Row4Iteration1
Row5Iteration1
Row1Iteration2
Row2Iteration2
Row3Iteration2
etc...

Does anyone know of a way to do this or is this an impossible constraint of .csv files? Is there another way, besides .csv, that I may be able to do this and still manipulate with Excel?

Answer 1

I hope this example helps you:

# of course you should read the file someway
s = """
Row1Iteration1, Row1Iteration2, Row1Iteration3
Row2Iteration1, Row2Iteration2, Row2Iteration3
Row3Iteration1, Row3Iteration2, Row3Iteration3
Row4Iteration1, Row4Iteration2, Row4Iteration3
Row5Iteration1, Row5Iteration2, Row5Iteration3
"""
ncols = 3

iterations = []
for line in s.strip().split('\n'):
    iterations.append([l.strip() for l in line.split(',')])

with open('output.csv', 'w') as out:
    for col in xrange(ncols):
        for it in iterations:
            print it[col]
            out.write(col)