Replacing Values with Other Values Using CSV Module In Python

Question

I am fairly inexperienced with the csv module in Python and was wondering if anyone could give any pointers. I have been looking through many other questions regarding this question but have come up with no answers for mine.

All I want to do is alter values, in which case it would be "n/a" and replace it with 0 in my csv file. These n/a values are within all columns so I can't pinpoint it to one specific column.

This is my code so far:

with open("MyCSV.csv","rb") as infile,open("Write.csv","wb") as outfile:
    reader= csv.reader(infile)
    writer= csv.writer(outfile)
    conversion= set('(n/a)')
    for row in reader:
        newrow=[''.join('0' if c in conversion else c for c in entry)for       entry in row]
        writer.writerow(newrow)

The issue I have come across in my result is that any a or n is transformed to a 0. This is obviously because it is being read that every 'n' or 'a' should be converted.

Thanks for any help someone can give.

Marius · Accepted Answer · 2015-04-07 02:10:05Z

1

set takes a sequence and uses all the items in that sequence to make the set. Since strings are sequences, what you end up with is:

set('(n/a)')
Out[7]: {'(', ')', '/', 'a', 'n'}

i.e. each individual character as an item. If you want the set to have one item, the full (n/a) string, then make a list with one item:

set(['(n/a)'])
Out[8]: {'(n/a)'}

answered Apr 7, 2015 at 2:10

Marius

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2 Comments

DSM Over a year ago

This is true, but the OP will still need to change the newrow line. Right now the OP is looping over characters when that's probably not intended.

Will B Over a year ago

This helps me understand it better, but it still does not work for me.

Amit · Accepted Answer · 2015-04-07 03:08:30Z

1

Here's a way to do using csv module

with open("MyCSV.csv","rb") as infile,open("Write.csv","wb") as outfile:
    reader = csv.reader(infile)
    writer = csv.writer(outfile)
    for row in reader:
        row = [x.replace('n/a', '0') if x == 'n/a' else x for x in row]
        writer.writerow(row)

Regex might be a better option here, something like this:

import re
with open("MyCSV.csv", "rb") as f1:
    lines = f1.read()
    for line in re.sub('n/a', '0', lines):
        print line,

edited Apr 7, 2015 at 3:08

answered Apr 7, 2015 at 2:10

Amit

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1 Comment

Will B Over a year ago

I've never used Regex before but using this script didn't seem to work. Would you not have to write it to a csv at some point, considering we would only be reading from my original file in this script?

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