map_along_dim: Apply a function across subsets along an array dimension

In listarrays: A Toolbox for Working with R Arrays in a Functional Programming Style

Apply a function across subsets along an array dimension

Description

map_along_dim(X, dim, func) is a simple wrapper around split_along_dim(X, dim) %>% map(func). It is conceptually and functionally equivalent to base::apply(), with the following key differences:

• it is guaranteed to return a list (base::apply() attempts to simplify the output to an array, sometimes unsuccessfully, making the output unstable)

• it accepts the compact lambda notation ~.x just like in purrr::map (and modify_along_dim())

Usage

map_along_dim(X, .dim, .f, ...)

map_along_rows(X, .f, ...)

map_along_cols(X, .f, ...)

Arguments

X	an R array
.dim	which dimension to map along. Passed on to split_along_dim(), and accepts all the same inputs. Valid inputs include positive integers (index position(s) of dimension), negative integers (index positions(s) of dimensions, counting from the back), or character vector (corresponding to array dimnames)
.f	A function, string of a function name, or purrr style compact lambda syntax (e.g, ~.x + 1)
...	passed on to .f()

Value

An R list

Examples

X <- matrix2(letters[1:15], ncol = 3)

apply(X, 1, function(x) paste(x, collapse = ""))   # simplifies to a vector
map_along_dim(X, 1, ~paste(.x, collapse = ""))     # returns a list

identical(
  map_along_rows(X, identity),
  map_along_dim(X, 1, identity)) # TRUE

identical(
  map_along_cols(X, identity),
  map_along_dim(X, -1, identity)) # TRUE

listarrays documentation built on May 29, 2024, 6:43 a.m.