Summing values of a pandas data frame given a list of columns [duplicate]

Question

Given a dataframe as follows:

x1 x2 x3 x4 x5 x6
1  2  3  4  5  6
3  4  5  6  3  3
1  2  3  6  1  2 

How could i create a new columns of 'sum' that just adds x1 + x3 + x4

x1 x2 x3 x4 x5 x6
1  2  3  4  5  6
3  4  5  6  3  3
1  2  3  6  1  2 

In my actual dataframe i have about 100 columns, so is there a way to do this without having to manually write x1 + x3 + ... + xn

e.g. given a list [x1, x3, x4.. xn] df['sum'] = sum(df[list]) ? Any help appreciated, thanks.

Answer 1

You can use subset of df and sum:

print df
   x1  x2  x3  x4  x5  x6
0   1   2   3   4   5   6
1   3   4   5   6   3   3
2   1   2   3   6   1   2

print df[['x1', 'x3', 'x4']]
   x1  x3  x4
0   1   3   4
1   3   5   6
2   1   3   6

li =  ['x1', 'x3', 'x4']
print df[li]
   x1  x3  x4
0   1   3   4
1   3   5   6
2   1   3   6

print df[li].sum()
x1     5
x3    11
x4    16
dtype: int64

print df[li].sum(axis=1)
0     8
1    14
2    10
dtype: int64