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to add column values in a specific manner in a csv file using python

Answer 1

A:

Have a look at the csv module. What you want to do is open the file with a csv.reader. Then you iterate over the file, one row at the time. You accumulate the results of the additions into a temporary list. When you are done, you write this list to a new csv.writer.

You might need to define a dialect as you are not really using CSV but some tab-delimited format.

Ranieri 2010-07-12 07:59:15

even if i read one row at a time, how do i accumulate the results for l1 alone, l2 alone and so on.... and this is necessarily comma separated i ve just given the table like this for better understanding..

newbie 2010-07-12 08:03:20

I can, but I won't. Accumulation is basic programming practice.

Ranieri 2010-07-12 08:09:36

i ve done some editing to the above table... i have now managed to get it in the above format... will this help??

newbie 2010-07-12 08:11:03

can you atleast give me more instructions on how to do this... i really can't get the hang of it...

newbie 2010-07-12 08:37:43

i don't mean to read it row wise... i want to read it column wise... can this be done by comparing title2 column's data?

newbie 2010-07-12 08:41:47

Answer 2

+1 A:

Something like this should work. It takes an input in the form

title,title2,h1,h2,h3
l1.1,l1,1,1,0
l1.2,l1,0,1,0
l1.3,l1,1,0,1
l2.1,l2,0,0,1
l2.2,l2,1,0,1
l3.1,l3,0,1,1
l3.2,l3,1,1,0
l3.3,l3,1,1,0
l3.4,l3,1,1,0

and outputs

title2,h1,h2,h3
l1,2,2,1
l2,1,0,2
l3,3,4,1

Tested with Python 3.1.2. In Python 2.x you'll need to change the open() calls to use binary mode, and drop the newline="" bit). You can also drop the call to list() since in Python 2.x, map() already returns a list.

import csv
import operator

reader = csv.reader(open("test.csv", newline=""), dialect="excel")
result = {}

for pos, entry in enumerate(reader):
    if pos == 0:
        headers = entry
    else:
        if entry[1] in result:
            result[entry[1]] = list(map(operator.add, result[entry[1]], [int(i) for i in entry[2:]]))
        else:
            result[entry[1]] = [int(i) for i in entry[2:]]

writer = csv.writer(open("output.txt", "w", newline=""), dialect="excel")
writer.writerow(headers[1:])

keys = sorted(result.keys())
for key in keys:
    output = [key]
    output.extend(result[key])
    writer.writerow(output)

Tim Pietzcker 2010-07-12 09:48:26

i m using python 2.7... i ve changed the open() part to "open('test.csv','rb'))... but i am getting a syntax error with the "result[entry[1]] = list(map(operator.add, result[entry[1]], [int(i) for i in entry[2:]]))" line12.... any modification i might have to make??

newbie 2010-07-12 10:29:35

Ah yes, remove the `list()`, that's only needed in Python 3 since `map` returns a view instead of a list in Python 3.

Tim Pietzcker 2010-07-12 10:53:52

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