how do I divide each number by sum of each row in python

Question

how do I divide each number by the sum? (skipping zeros) I'd like to divide each row by it's sum

ex. 0(number on 0 column)/2(sum column)

0 1 2 3 4 5 6 7 ... sum
0 0 0 0 1 0 0 0 ...  2

result

0 1 2 3 4   5 6 7 ... sum
0 0 0 0 0.5 0 0 0      2

Answer 1

You can try something like this

#### this will contain everyother column except sum
required_columns = df.columns[~df.contains.str.contains('sum')]
### regex can also be used with contains , I m here assuming you all other column will not be named as sum , for which the division is to be performed


for col in required_colums:
    print (f'---------- {col} --------')
    df.loc[:,col] = df.loc[:,col]/df.loc[:,'sum']

Answer 2

You can also give this to get the same answer.

df.iloc[:,:-1] = df.apply(lambda r: r/r['sum'] if r['sum'] != 0 else r['sum'],axis=1).round(2)

The output of this will be:

Source df:

   0  1  2  3  4  5  6  7  sum
0  0  0  0  0  1  0  0  0    2
1  0  0  0  6  0  0  0  0   18
2  0  0  0  0  1  0  0  0    0
3  0  0  3  0  0  0  4  0    1

This will result in:

     0    1    2     3    4    5    6    7  sum
0  0.0  0.0  0.0  0.00  0.5  0.0  0.0  0.0    2
1  0.0  0.0  0.0  0.33  0.0  0.0  0.0  0.0   18
2  0.0  0.0  0.0  0.00  0.0  0.0  0.0  0.0    0
3  0.0  0.0  3.0  0.00  0.0  0.0  4.0  0.0    1

Here is the explanation for the above code:

On the left hand side of the equation, I have iloc. You can get more documentation of iloc here.

df.iloc[:,:-1]

Here I am picking all the rows (first set of :,). The second set is the columns. I am having the right hand side computational value assigned to all but the last column which is the sum column. I dont want to replace that value.

df.apply will process the dataframe one row at a time. see examples of df.apply here

Here I am picking the first row (r) and processing it. You wanted to compute column (x) / column('sum'). Thats what i am doing. It does this for each column in the row.

I am also checking if r['sum'] is not equal to zero to avoid division by zero error. If the value of r['sum'] is zero, then i am sending r['sum'] (or zero).

A DataFrame object has two axes: “axis 0” and “axis 1”. “axis 0” represents rows and “axis 1” represents columns. I am using axis = 1 to traverse through the row instead of values in each column.

Hope this explanation helps.