which-type: Where are certain types of columns?
In bgreenwell/bmisc: Miscellaneous R Functions

Determines the names or locations (i.e., index) of particular types of columns.

which_numeric(x, names = TRUE)

which_factor(x, names = TRUE)

which_character(x, names = TRUE)

which_integer(x, names = TRUE)

`x`	A data frame (ideally), but list-like objects should work too.
`names`	Logical indicating whether to return names (`TRUE`) or indexes `FALSE`. Default is `TRUE`.

which_numeric(iris)
which_factor(iris)
d <- data.frame(x = 1:3, y = c("a", "b", "c"), stringsAsFactors = FALSE)
which_integer(d)
which_numeric(d)
which_character(d)