Question

I have tab delimited data that I am exporting a select few columns into another file. I have:

a b c d
1 2 3 4
5 6 7 8 
9 10 11 12

and I get:

b, d
b, d
2, 4
b, d
2, 4
6, 8
b, d
2, 4
6, 8
10, 12
......

I want:

b, d
2, 4
6, 8 
10, 12

My code is

f=open('data.txt', 'r')
f1=open('newdata.txt','w')
t=[]
for line in f.readlines():
    line =line.split('\t')
    t.append('%s,%s\n' %(line[0], line[3]))
    f1.writelines(t)

What am I doing wrong??? Why is it repeating?

PLease help

Thanks!!

Answer 1

The indentation is wrong so you are writing the entire array t on every iteration instead of only at the end. Change it to this:

t=[]
for line in f.readlines():
    line = line.split('\t')
    t.append('%s,%s\n' % (line[0], line[3]))
f1.writelines(t)

Alternatively you could write the lines one at a time instead of waiting until the end, then you don’t need the array t at all.

for line in f.readlines():
    line = line.split('\t')
    s = '%s,%s\n' % (line[0], line[3])
    f1.write(s)