How to fill a specific position missing value in pandas Dataframe

Question

I have a pandas Dataframe with 15 x 15 dimensions.

I am trying to fill the missing values using if statement. I want to fill the mirrored position of filled values. For example, if z.values[0, 0] == 1 then I want to fill the z.values[15, 15] value equal to 0 and vise versa. I am using this code:

    if z.values[0, 0] == 1:
        z.values[15, 15].fillna() == 0
    else:
        z.values[15, 15].fillna() == 1

Note: This is just for z.values[0, 0] I also want all the indexing to have the above mentioned coding using a for loop or something else.

Answer 1

You could first invert your dataframe by reversing the index and columns:

>>> df2 = df.loc[df.index[::-1], df.columns[::-1]]

Then, we replace 0s with 1s and 1s with 0s:

>>> df2 = df2.replace({0: 1, 1: 0})

Now, use those values to fill your datafrme only where the value is currently null:

>>> df[df.isnull()] = df2.values

For example, for this sample input:

    F4   F3   F2   F1
F4   1  1.0  1.0  1.0
F3   0  1.0  1.0  NaN
F2   1  1.0  NaN  NaN
F1   1  NaN  NaN  NaN

The output is this:

    F4   F3   F2   F1
F4   1  1.0  1.0  1.0
F3   0  1.0  1.0  0.0
F2   1  1.0  0.0  1.0
F1   1  0.0  0.0  0.0