Reshaping CSV columns in python

Question

I have my data in this form

and the required form of data is

Can anybody help me in this regard?

---

The content of the initial CSV file as text is:

var1,var2,col1,col2,col3
a,f,1,2,3
b,g,4,5,6
c,h,7,8,9
d,i,10,11,12

Answer 1

You can do it directly with the csv module. You just read from the initial file, and write up to 3 rows per initial row into the resulting file:

with open('in.csv') as fdin, open('out.csv', 'w', newline='') as fdout:
    rd = csv.reader(fdin)
    wr = csv.writer(fdout)
    header = next(rd)       # read and process header
    _ = wr.writerow(header[:2] + ['columns',''])
    for row in rd:                                  # loop on rows
        for i in range(3):                          # loop on the 3 columns
            try:   
                row2 = row[:2] + ['col{}'.format(i+1), row[2 + i]]
                _ = wr.writerow(row2)
            except IndexError:                      # prevent error on shorter line
                break

If you intend to do heavy data processing, you should contemplate using the Pandas module.

With the data sample, it gives:

var1,var2,columns,
a,f,col1,1
a,f,col2,2
a,f,col3,3
b,g,col1,4
b,g,col2,5
b,g,col3,6
c,h,col1,7
c,h,col2,8
c,h,col3,9
d,i,col1,10
d,i,col2,11
d,i,col3,12