Sum a csv column in python

Question

I'm trying to make a sum of a column in a csv file. The file looks like:

Date  Value
2012-11-20  12
2012-11-21  10
2012-11-22  3

This can be in the range of hundreds of rows. I need to get the total of Value (in this case it would be 25) printed on to a terminal. I so far have some code but it's resulting in a much smaller figure than it should sum. When troubleshooting it, I did a print of the sum and realized that instead of summing 12 + 10 + 3, it actually breaks the numbers in each column and sums as 1 + 2 + 1 + 0 + 3, which obviously equals to a much smaller total. Here's my code, if someone could make a recommendation would be great!

with open("file.csv")) as fin:
  headerline = fin.next()
  total = 0
  for row in csv.reader(fin):
    print col # for troubleshooting
    for col in row[1]:
      total += int(col)
  print total

Martijn Pieters · Accepted Answer · 2023-02-23 00:27:41Z

12

The csv module loops over your rows one by one, there is no need to then loop over the column. Just sum int(row[1]):

with open("file.csv") as fin:
    headerline = next(fin)
    total = 0
    for row in csv.reader(fin):
        total += int(row[1])
    print(total)

You can use a shortcut with a generator expression and the sum() built-in function:

with open("file.csv") as fin:
    next(fin)
    total = sum(int(r[1]) for r in csv.reader(fin))

Note that in Python, strings are sequences too, so when you do for col in row[1]: you are looping over the individual characters of row[1]; so for your first row that'd be 1 and 2:

>>> for c in '123':
...     print(repr(c))
...
'1'
'2'
'3'

edited Feb 23, 2023 at 0:27

answered Nov 22, 2012 at 16:51

Martijn Pieters

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Comments

ahaan abrar · Accepted Answer · 2021-08-21 07:29:05Z

3

You can use pandas instead.

import pandas as pd
df2=pd.read_csv('file.csv')
df2['Value'].sum()

edited Aug 21, 2021 at 7:29

answered Aug 21, 2021 at 7:24

ahaan abrar

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Comments

Elijah · Accepted Answer · 2023-02-23 04:12:54Z

0

import csv

csv_file = 'file.csv'

with open(csv_file) as f:
    total = sum(int(r['Value']) for r in csv.DictReader(f))

answered Feb 23, 2023 at 4:12

Elijah

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2 Comments

niaei Over a year ago

And what if you had a fractional number?

Elijah Over a year ago

Is that supposed to be a gotcha? You'd use float instead of int

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