How to replace a particular comma in a CSV file using Python?

Question

I have quite a big CSV file where lines have varying length:

215080,49,3,0.0,22,42,0.0
215082,49,3,0.0,22,43,59.999 
215083,49,3,0.0,22,45,0.0
215085,49,3,0.0,22,46,59.999
215086,49,3,0.0,22,48,0.0
215087,49,3,0.0,22,49,0.001
215088,49,3,0.0,22,49,59.999
215089,49,3,0.0,22,51,0.0
215090,49,3,0.0,22,52,0.001
215688,49,1,59.999,22,49,0.001
215689,49,1,59.999,22,49,59.999
215690,49,1,59.999,22,51,0.0
215691,49,1,59.999,22,52,0.001
216291,49,1,0.001,22,51,0.0
216292,49,1,0.001,22,52,0.001
216293,49,1,0.001,22,52,59.999

I would like to replace, for example, only the fourth comma (,) in every line with a semicolon (;). How can I do this most efficiently?

The fourth comma only, or the fourth, eighth, 12th, and so on? — Warren P
– Warren P, Commented Dec 21, 2011 at 23:18
@Warren P Sorry if it is not clear, the fourth coma only as You can see, the fourth coma is separator between coordinates, latitude and longitude — daikini
– daikini, Commented Dec 23, 2011 at 20:02
English tip: "the fourth" is clear. Just the 4th. "Every fourth" means 4th, 8th, 12th, 16th, and so on. — Warren P
– Warren P, Commented Dec 23, 2011 at 20:12

S.Lott · Accepted Answer · 2011-12-24 13:03:29Z

7

import csv
with open('source.csv','rb') as source:
    rdr= csv.reader( source )
    with open('revised.csv','wb') as target:
        wtr= csv.writer( target )
        for r in rdr:
            wtr.writerow( (r[0], r[1], r[2], '{0};{1}'.format(r[3],r[4]), r[5], r[6]) )

edited Dec 24, 2011 at 13:03

answered Dec 21, 2011 at 23:12

S.Lott

393k83 gold badges520 silver badges791 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

daikini Over a year ago

Thanks for Your solution...although I had to change the last line to: wtr.writerow( (r[0], r[1], r[2], '{0};{1}'.format(r[3],r[4]), r[5], r[6]) )

John Y · Accepted Answer · 2011-12-21 23:24:46Z

4

You could do something like this on each line of input.

tmp = line.split(',', 4)
newline = '%s;%s' % (','.join(tmp[:4]), tmp[4])

edited Dec 21, 2011 at 23:24

John Y

14.6k2 gold badges51 silver badges76 bronze badges

answered Dec 21, 2011 at 23:11

Lara Bailey

802k110 gold badges650 silver badges667 bronze badges

15 Comments

Warren P Over a year ago

This would work unless it's a true CSV file with things like embedded quotes around fields that contain commas inside the literal string values. It works for the inputs that the OP specified, for instance.

Lara Bailey Over a year ago

@WarrenP: What do you mean by a "true" CSV file? I didn't think that there was a standard. Software that I've seen uses lots of different conventions for trying to have fields with commas in them a "CSV".

John Y Over a year ago

@Charles: There may not be One True CSV, but Python's csv module is configurable enough to understand several variations, including Excel's, which I would think is the dominant variant of CSV in the real world.

Cesar Canassa Over a year ago

+1 I wasn't aware that you could pass a second parameter to split.

Cesar Canassa Over a year ago

This code more readable and much faster than the csv version. If you know that input file doesn't contains extra commas you should go with the split version and don't over engineer stuff.

|

Cesar Canassa · Accepted Answer · 2011-12-21 23:22:40Z

2

Another approach

>>> a = '215080,49,3,0.0,22,42,0.0'
>>> b = a.split(',')
>>> ','.join(b[0:3] + [b[3] + ';'  + b[4]] + b[5:])
'215080,49,3,0.0;22,42,0.0'

answered Dec 21, 2011 at 23:22

Cesar Canassa

20.5k13 gold badges68 silver badges70 bronze badges

Collectives™ on Stack Overflow

How to replace a particular comma in a CSV file using Python?

3 Answers 3

1 Comment

15 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

15 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related