On Thu, 03 Sep 2009 03:21:25 -0700, Olli Virta wrote:
> What I need to do, is put the three rows that goes together and belong
> to
> certain subject, on a one line in the output textfile. And the next
> three
> rows again on a one new line. And that goes with the rest of the data to
> the end of the new file.
>
> Can't figure out a working loop structure to handle this.
The basic algorithm is:
- grab three lines from the input file
- write to the output file
- repeat until done
There are lots of ways to do this. Here's one:
# untested
out = file(outfile, 'w')
in_ = file(infile, 'r')
while True:
# Grab three lines.
a = in_.readline()
if a == '':
# Nothing more to read, we're done.
break
b = in_.readline()
c = in_.readline()
out.write(a.rstrip() + ' ')
out.write(b.rstrip() + ' ')
out.write(c.rstrip() + '\n')
out.close()
in_.close()
Here's another version:
# untested
out = file(outfile, 'w')
accumulator = []
for line in file(infile, 'r'):
if len(accumulator) == 3:
out.write("%s %s %s\n" % tuple(accumulator))
accumulator = []
accumulator.append(line.rstrip())
if accumulator:
out.write("%s %s %s\n" % tuple(accumulator))
out.close()
Chris has posted another method, using itertools. That's probably faster
for very large files, but less readable.
--
Steven
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