Is there any way to reference the last column within mutate so that you can do an operation on it? For instance:
library(dplyr)
library(tidyr)
dat <- data.frame(
col1 = c(1, 1, 1),
col2 = c(0, 1, 0),
col3 = c(2, 0, 2)
)
## what i was thinking:
dat %>%
mutate(col1_bigger_than_col3 = col1 > last_col())
#> Error in `mutate()`:
#> ! Problem while computing `col1_bigger_than_col3 = col1 > last_col()`.
#> Caused by error:
#> ! `last_col()` must be used within a *selecting* function.
#> ℹ See <https://tidyselect.r-lib.org/reference/faq-selection-context.html>.
#> Backtrace:
#> ▆
#> 1. ├─dat %>% mutate(col1_bigger_than_col3 = col1 > last_col())
#> 2. ├─dplyr::mutate(., col1_bigger_than_col3 = col1 > last_col())
#> 3. ├─dplyr:::mutate.data.frame(., col1_bigger_than_col3 = col1 > last_col())
#> 4. │ └─dplyr:::mutate_cols(.data, dplyr_quosures(...), caller_env = caller_env())
#> 5. │ ├─base::withCallingHandlers(...)
#> 6. │ └─mask$eval_all_mutate(quo)
#> 7. └─tidyselect::last_col()
#> 8. ├─vars %||% peek_vars(fn = "last_col")
#> 9. └─tidyselect::peek_vars(fn = "last_col")
#> 10. └─rlang::abort(msg, call = NULL)
## output i want
dat %>%
mutate(col1_bigger_than_col3 = col1 > col3)
#> col1 col2 col3 col1_bigger_than_col3
#> 1 1 0 2 FALSE
#> 2 1 1 0 TRUE
#> 3 1 0 2 FALSE
>Solution :
We may use last_col() in select or in across
library(dplyr)
dat %>%
mutate(col1_bigger_than_col3 = col1 > across(last_col())[[1]])
-output
col1 col2 col3 col1_bigger_than_col3
1 1 0 2 FALSE
2 1 1 0 TRUE
3 1 0 2 FALSE
Or update with .names after doing the calculation inside across
dat %>%
mutate(across(last_col(), ~ col1 > .x,
.names = "col1_bigger_than_{.col}"))
col1 col2 col3 col1_bigger_than_col3
1 1 0 2 FALSE
2 1 1 0 TRUE
3 1 0 2 FALSE