Apply Function With Multiple Arguments to Pandas Dataframe

Question

How to apply a function with multiple arguments to a dataframe? My function is something like this:

def test(a,b,c,d,e,f):
    if b == 1 :
        if d == 0 :
            return a-f
    if b == 0 :
        if c == 1 :
            return a-e

My sample data is this :

a	b	c	d	e	f
2021-04-29 22:04:000	1	0.0	0.0	2021-04-28 10:10:00	2021-04-29 23:14:00
2021-06-10 06:00:00	0	1.0	1.0	2021-06-09 23:00:00	2021-06-11 00:29:00
2021-06-09 23:00:00	1	0.0	0.0	2021-06-06 11:00:00	2021-06-10 06:00:00
2021-06-06 11:00:00	0	1.0	1.0	2021-06-06 08:00:00	2021-06-09 23:00:00
2021-06-06 08:00:00	1	0.0	0.0	2021-06-06 04:00:00	2021-06-06 11:00:00

I tried this line of code and then shows error : the code:

df['dt'] = df.apply(test, args=('a','b','c','d','e','f'), axis=1)

the error:

test() takes 6 positional arguments but 7 were given

I don't understand why it detected as 7 arguments when in my code only six.

The first argument is always populated with row, any values passed as args are additional. In this case you've passed the literal characters a-f as additional arguments. — Henry Ecker
– Henry Ecker ♦, Commented Jun 26, 2021 at 23:26

Kato · Accepted Answer · 2021-06-26 22:17:33Z

1

You could try changing your function like so:

def test(row):
    a,b,c,d,e,f = row
    if b == 1 :
        if d == 0 :
            return a-f
    if b == 0 :
        if c == 1 :
            return a-e

Then modify the way you apply the function like so:

df['dt'] = df.apply(test, axis=1)

answered Jun 26, 2021 at 22:17

Kato

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4 Comments

Ridwan Nurzeha Over a year ago

How to apply if the column is not in the same order, have different name, or have other columns between the arguments?

Kato Over a year ago

the names of the columns make no difference since test() is unpacking each row into 6 variables. The value of row a will go into variable a, the value of row b will go into variable b, and so on. @RidwanNurzeha

Ridwan Nurzeha Over a year ago

so in other words, I must match the order and number of columns between the function and dataframe?

Kato Over a year ago

I just realized I said the wrong thing, I mean to say "The value of column a will go into variable a, the value of column b, will go into variable b..." etc. But yes, the number of variables you use to unpack the row must match the order and number of columns in the data frame. @RidwanNurzeha

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