Conditionals (if_else)

from siuba.data import penguins
from siuba import _, summarize, group_by, if_else, transmute, case_when

penguins

	species	island	bill_length_mm	bill_depth_mm	flipper_length_mm	body_mass_g	sex	year
0	Adelie	Torgersen	39.1	18.7	181.0	3750.0	male	2007
1	Adelie	Torgersen	39.5	17.4	186.0	3800.0	female	2007
...	...	...	...	...	...	...	...	...
342	Chinstrap	Dream	50.8	19.0	210.0	4100.0	male	2009
343	Chinstrap	Dream	50.2	18.7	198.0	3775.0	female	2009

344 rows × 8 columns

if_else for two cases

Use the if_else() when values depend only on two cases—like whether some condition is True or False. This is similar to a Python if else statement, but applies to each value in a column.

Basics

if_else(penguins.bill_length_mm > 40, "long", "short")

0      short
1      short
       ...  
342     long
343     long
Length: 344, dtype: object

Use in a verb

transmute(
    penguins,
    bill_length = if_else(_.bill_length_mm > 40, "long", "short")
)

	bill_length
0	short
1	short
...	...
342	long
343	long

344 rows × 1 columns

case_when for many cases

The case_when() function is a more general version of if_else(). It lets you check as many cases as you want, and map them to resulting values.

Basics

case_when(penguins, {
    _.bill_depth_mm <= 18: "short",
    _.bill_depth_mm <= 19: "medium",
    _.bill_depth_mm > 19: "long"
})

0      medium
1       short
        ...  
342    medium
343    medium
Length: 344, dtype: object

Use in a verb

# also works
penguins >> case_when({ ... })

Set default when no match

Use a True as the final case, in order to set a value when no other cases match.

case_when(penguins, {
    _.bill_depth_mm.between(18, 19): "medium",
    True: "OTHER"
})

0      medium
1       OTHER
        ...  
342    medium
343    medium
Length: 344, dtype: object

Note that this works because—for each value—case_when checks for the first matching condition. The final True condition guarantees that it will always be a match.