Pandas, summing values in a row to form a "totals" column

Question

So I’ve been trying to get the sum of my rows and have them add into a new column. My data is something along the lines of:

     Animal  num1  num2 
0    22-14  36.6   213      
1    39-14  42.44  141      
2    40-14  39     157

I’ve tried things such as:

df['sum'] = df['num1'] + df['num2']

But that just combines the information together, it doesn’t sum it. Is there a way to do this?

Asked By: Michael S.

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Source

Answer 1

Your issue is that your columns are actually strings, not numbers. When you try to sum the columns, the strings just get concatenate (e.g. 'cat' + 'dog' becoming 'catdog').

You can convert them to numbers using pandas.DataFrame.convert_objects.

import pandas as pd
from io import StringIO

s = """     Animal  num1  num2 
0    22-14  36.6   213      
1    39-14  42.44  141      
2    40-14  39     157"""

df = pd.read_csv(StringIO(s), sep='s+', dtype=str)

# You can ignore the code above this point, I was just re-creating your DataFrame.
df = df.convert_objects(convert_numeric=True)

After this, it should work exactly as you said above, so:

df['sum'] = df['num1'] + df['num2']

print(df)
#  Animal   num1  num2     sum
#0  22-14  36.60   213  249.60
#1  39-14  42.44   141  183.44
#2  40-14  39.00   157  196.00

Answered By: Ffisegydd

Answer 2

The sum command takes an axis argument that can be used to sum either columns (1) or rows(0).

df = pd.DataFrame({'a':[4,5,2],'b':[5,2,9]})
df['c'] = df.sum(axis=1)

This method only accept numbers, you first column is a string so you will have to parse that. For example if you want to remove the hyphen from the numbers you could use the command:

df['Animal'] = df['Animal'].apply(lambda x: int(x.replace('-','')))

Or if you want to ignore that first column entirely you can simply not include it .

df['sum'] = df.iloc[:,1:].sum(axis = 1)

Answered By: champagne_campaign

Pandas, summing values in a row to form a "totals" column

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