update_by: update columns conditionally
In schmettow/mascutils: Various utility functions of Martin Schmettow

Description Usage Arguments Value Author(s) Examples

View source: R/data_manipulation.R

update columns conditionally

1	update_by(D, by, ...)

`D`	data frame
`...`	expressions
`filter`	predicate function (like dplyr::filter)

data frame

Applies mutations to the filtered group, only.

Martin Schmettow

D <- tribble(~group, ~value,  1, 4, 1, 9, 2, -4, 2, -9)

D %>% mutate(value = if_else(group == 1, sqrt(value), value))
## Produces NaNs, because sqrt() is evaluated before selection

D %>% mutate_by(group == 1, value = sqrt(value))
## sqrt() is only evaluated