Place a small array into a big array-CodePudding

I have 2 arrays; one is small array and second is big array as follows,

import pandas as pd
import numpy as np
dat1 = np.array([2, 3 ,4 ,4 ,3 ,2, 2, 4 ,3 ,4 ,4, 3])
dat2 = np.array([1, 4 ,4, 4, 2 ,1, 3 ,3 ,2, 3, 3, 1])
small_array = pd.crosstab(dat1, dat2)

big_array = pd.DataFrame(np.zeros(6*6).reshape(6,6), columns=[1,3,4,2,6,5], index=[3,4,1,2,5,6])

Now I want to place small_array into big_array matching the rownames and colnames between both arrays.

Is there any easy way to perform this?

Any pointer will be very helpful

CodePudding user response：

You can update big_array in-place:

big_array.update(small_array)
print(big_array)

If you want to create a new DataFrame, you can use combine_first:

out = small_array.combine_first(big_array)

Output:

     1    3    4    2    6    5
3  1.0  0.0  1.0  2.0  0.0  0.0
4  0.0  3.0  2.0  0.0  0.0  0.0
1  0.0  0.0  0.0  0.0  0.0  0.0
2  2.0  1.0  0.0  0.0  0.0  0.0
5  0.0  0.0  0.0  0.0  0.0  0.0
6  0.0  0.0  0.0  0.0  0.0  0.0

CodePudding user response：

Let us try reindex_like

out = small_array.reindex_like(big_array).fillna(0)
Out[494]: 
     1    3    4    2    6    5
3  1.0  0.0  1.0  2.0  0.0  0.0
4  0.0  3.0  2.0  0.0  0.0  0.0
1  0.0  0.0  0.0  0.0  0.0  0.0
2  2.0  1.0  0.0  0.0  0.0  0.0
5  0.0  0.0  0.0  0.0  0.0  0.0
6  0.0  0.0  0.0  0.0  0.0  0.0