purrr (version 0.2.0)

dmap: Map over the columns of a data frame

Description

dmap() is just like map() but always returns a data frame. In addition, it handles grouped or sliced data frames.

Usage

dmap(.d, .f, ...)
dmap_at(.d, .at, .f, ...)
dmap_if(.d, .p, .f, ...)

Arguments

.d

A data frame.

.f

A function, formula, or atomic vector.

If a function, it is used as is.

If a formula, e.g. ~ .x + 2, it is converted to a function with two arguments, .x or . and .y

...

Additional arguments passed on to .f.

.at

A character vector of names or a numeric vector of positions. Only those elements corresponding to .at will be modified.

.p

A single predicate function, a formula describing such a predicate function, or a logical vector of the same length as .x. Alternatively, if the elements of .x are themselves lists of objects, a string indicating the name of a lo

Details

dmap_at() and dmap_if() recycle length 1 vectors to the group sizes.

Examples

# dmap() always returns a data frame:
dmap(mtcars, summary)

# dmap() also supports sliced data frames:
sliced_df <- mtcars[1:5] %>% slice_rows("cyl")
sliced_df %>% dmap(mean)
sliced_df %>% dmap(~ .x / max(.x))

# This is equivalent to the combination of by_slice() and dmap()
# with 'rows' collation of results:
sliced_df %>% by_slice(dmap, mean, .collate = "rows")