Find sum of the column values based on some other column - python-2.7

Question

I have a input file like this:
j,z,b,bsy,afj,upz,343,13,ruhwd
u,i,a,dvp,ibt,dxv,154,00,adsif
t,a,a,jqj,dtd,yxq,540,49,kxthz
j,z,b,bsy,afj,upz,343,13,ruhwd
u,i,a,dvp,ibt,dxv,154,00,adsif
t,a,a,jqj,dtd,yxq,540,49,kxthz
c,u,g,nfk,ekh,trc,085,83,xppnl
For every unique value of Column1, I need to find out the sum of column7
Similarly, for every unique value of Column2, I need to find out the sum of column7
Output for 1 should be like:
j,686
u,308
t,98
c,83
Output for 2 should be like:
z,686
i,308
a,98
u,83
I am fairly new in Python. How can I achieve the above?

Answer 1

This could be done using Python's Counter and csv library as follows:
from collections import Counter
import csv
c1 = Counter()
c2 = Counter()
with open('input.csv') as f_input:
for cols in csv.reader(f_input):
col7 = int(cols[6])
c1[cols[0]] += col7
c2[cols[1]] += col7
print "Column 1"
for value, count in c1.iteritems():
print '{},{}'.format(value, count)
print "\nColumn 2"
for value, count in c2.iteritems():
print '{},{}'.format(value, count)
Giving you the following output:
Column 1
c,85
j,686
u,308
t,1080
Column 2
i,308
a,1080
z,686
u,85
A Counter is a type of Python dictionary that is useful for counting items automatically. c1 holds all of the column 1 entries and c2 holds all of the column 2 entries. Note, Python numbers lists starting from 0, so the first entry in a list is [0].
The csv library loads each line of the file into a list, with each entry in the list representing a different column. The code takes column 7 (i.e. cols[6]) and converts it into an integer, as all columns are held as strings. It is then added to the counter using either the column 1 or 2 value as the key. The result is two dictionaries holding the totaled counts for each key.

Answer 2

You can use pandas:
df = pd.read_csv('my_file.csv', header=None)
print(df.groupby(0)[6].sum())
print(df.groupby(1)[6].sum())
Output:
0
c 85
j 686
t 1080
u 308
Name: 6, dtype: int64
1
a 1080
i 308
u 85
z 686
Name: 6, dtype: int64
The data frame should look like this:
print(df.head())
Output:
0 1 2 3 4 5 6 7 8
0 j z b bsy afj upz 343 13 ruhwd
1 u i a dvp ibt dxv 154 0 adsif
2 t a a jqj dtd yxq 540 49 kxthz
3 j z b bsy afj upz 343 13 ruhwd
4 u i a dvp ibt dxv 154 0 adsif
You can also use your own names for the columns. Like c1, c2, ... c9:
df = pd.read_csv('my_file.csv', index_col=False, names=['c' + str(x) for x in range(1, 10)])
print(df)
Output:
c1 c2 c3 c4 c5 c6 c7 c8 c9
0 j z b bsy afj upz 343 13 ruhwd
1 u i a dvp ibt dxv 154 0 adsif
2 t a a jqj dtd yxq 540 49 kxthz
3 j z b bsy afj upz 343 13 ruhwd
4 u i a dvp ibt dxv 154 0 adsif
5 t a a jqj dtd yxq 540 49 kxthz
6 c u g nfk ekh trc 85 83 xppnl
Now, group by column 1 c1 or column c2 and sum up column 7 c7:
print(df.groupby(['c1'])['c7'].sum())
print(df.groupby(['c2'])['c7'].sum())
Output:
c1
c 85
j 686
t 1080
u 308
Name: c7, dtype: int64
c2
a 1080
i 308
u 85
z 686
Name: c7, dtype: int64

Answer 3

SO isn't supposed to be a code writing service, but I had a few minutes. :) Without Pandas you can do it with the CSV module;
import csv
def sum_to(results, key, add_value):
if key not in results:
results[key] = 0
results[key] += int(add_value)
column1_results = {}
column2_results = {}
with open("input.csv", 'rt') as csvfile:
reader = csv.reader(csvfile)
for row in reader:
sum_to(column1_results, row[0], row[6])
sum_to(column2_results, row[1], row[6])
print column1_results
print column2_results
Results:
{'c': 85, 'j': 686, 'u': 308, 't': 1080}
{'i': 308, 'a': 1080, 'z': 686, 'u': 85}
Your expected results don't seem to match the math that Mike's answer and mine got using your spec. I'd double check that.