Dataframe list comprehension “zip(…)”: loop through chosen df columns efficiently with just a list of column name strings

Question

This is just a nitpicking syntactic question...

I have a dataframe, and I want to use list comprehension to evaluate a function using lots of columns.

I know I c

Answer 1

df.apply() is almost as slow as df.iterrows(), both are not recommended, see How to iterate over rows in a DataFrame in Pandas --> search for "An Obvious Example" of @cs95a and see the comparison graph. As the fastest ways (vectorization, Cython routines) are not easy to implement, the 3rd best and thus usually best solution is list comprehension:

# print 3rd col
def some_func(row):
    print(row[2])


df['result_col'] = [some_func(*row) for row in zip(df[['col_1', 'col_2',... ,'col_n']].to_numpy())]

or

# print 3rd col
def some_func(row):
    print(row[2])

df['result_col'] = [some_func(row[0]) for row in zip(df[['col_1', 'col_2',... ,'col_n']].to_numpy())]

or

# print 3rd col
def some_func(x):
    print(x)

df['result_col'] = [some_func(row[0][2]) for row in zip(df[['col_1', 'col_2',... ,'col_n']].to_numpy())]

See also:

• Memory efficient way for list comprehension of pandas dataframe using multiple columns
• list comprehension in pandas

EDIT:

Please use df.iloc and df.loc instead of df[[...]], see Selecting multiple columns in a pandas dataframe