Pandas: How to set values from another column based on conditions column-wise

I have a dataframe that has this shape:

The first two columns have the values I want to populate with the rest of the columns. The rest of the colums (col i…col z) should be populated with values from col A and col B depending on the value of each one. For example, the first row of col i has a B, so it should be populated with the value of col B at the same row (2).

I tried different functions for this, apply, applymap, but none of them are suitable for this use case.

The remaining table in this example should look like this:

>Solution :

Use indexing and map to replace letters:

df.iloc[:, 2:] = df.apply(lambda x: x[2:].map(x[:2]), axis=1)
print(df)

# Output:
   A  B  i  j  y  z
0  1  2  2  1  1  1
1  2  3  3  2  3  3

Setup:

df = pd.DataFrame({'A': [1, 2], 'B': [2, 3], 'i': ['B', 'B'],
                   'j': ['A', 'A'], 'y': ['A', 'B'], 'z': ['A', 'B']})
print(df)

# Output:
   A  B  i  j  y  z
0  1  2  B  A  A  A
1  2  3  B  A  B  B

Details:

For each row, apply the following function over index axis so x contains the whole row at each iteration:

Map the value from the third column (x[2:] <- i, j, y, z) to the index from the two first columns (x[:2] <- A, B) like a dictionary (a Series can act as dictionary, check the map method)

For the first iteration:

A    1  # <- index A
B    2  # <- index B
i    B  # <- value B
j    A  # <- value A
y    A  # <- value A
z    A  # <- value A
Name: 0, dtype: object