case when pandas column code example

Example 1: case statement in pandas

# If the row value in column 'is_blue' is 1 
# Change the row value to 'Yes' 
# otherwise change it to 'No'
df['is_blue'] = df['is_blue'].apply(lambda x: 'Yes' if (x == 1) else 'No') 


# You can also use mapping to accomplish the same result
# Warning: Mapping only works once on the same column creates NaN's otherwise
df['is_blue'] = df['is_blue'].map({0: 'No', 1: 'Yes'})

Example 2: pandas columns case when equivalent

df['c'] = np.select(
[
    (df['a'].isnull() & (df['b'] == 0))
], 
[
    1
], 
default=0 )