Pandas apply a function using index name and column name-CodePudding

Consider the dataframe:

data = pd.DataFrame(0, index=[1,2,3,4], columns=[1,2,3,4])
data    
    1   2   3   4
1   0   0   0   0
2   0   0   0   0
3   0   0   0   0
4   0   0   0   0

I want to fill the values using a function that takes two arguments. These two arguments will be the index name and the column name of the dataframe. How can I achieve this (using vectorization)?

def multiply(a, b):
    return a * b

I have been trying various combinations of data.apply(lambda x: x.apply(multiply, args=(x.name))) but could not make it work.

Any help is appreciated greatly.

CodePudding user response：

If use apply there are loops under the hood, so not vecorized solution, If need multiple index by columns names use numpy soluton like:

a = data.index.to_numpy() * data.columns.to_numpy()[:, None]
print (a)
[[ 1  2  3  4]
 [ 2  4  6  8]
 [ 3  6  9 12]
 [ 4  8 12 16]]

data[:] = data.index.to_numpy() * data.columns.to_numpy()[:, None]
print (data)
   1  2   3   4
1  1  2   3   4
2  2  4   6   8
3  3  6   9  12
4  4  8  12  16

CodePudding user response：

You can make your code work, using:

def multiply(a, b):
    return a * b

df = df.apply(lambda x: multiply(x.index, x.name))