Produce all combinations of list elements

These functions were deprecated in purrr 1.0.0 and are now defunct because they are slow and buggy, and we no longer think they are the right approach to solving this problem. Please use tidyr::expand_grid() instead.

Here is an example of equivalent usages for cross() and expand_grid():

data <- list(
  id = c("John", "Jane"),
  sep = c("! ", "... "),
  greeting = c("Hello.", "Bonjour.")
)

# With defunct `cross()`
data |> cross() |> map_chr(\(...) paste0(..., collapse = ""))

# With `expand_grid()`
tidyr::expand_grid(!!!data) |> pmap_chr(paste)

Usage

cross(.l, .filter = NULL)

cross2(.x, .y, .filter = NULL)

cross3(.x, .y, .z, .filter = NULL)

cross_df(.l, .filter = NULL)

Arguments

.l

A list of lists or atomic vectors. Alternatively, a data frame. cross_df() requires all elements to be named.

.filter

A predicate function that takes the same number of arguments as the number of variables to be combined.

.x, .y, .z

Lists or atomic vectors.

Value

cross2(), cross3() and cross() always return a list. cross_df() always returns a data frame. cross() returns a list where each element is one combination so that the list can be directly mapped over. cross_df() returns a data frame where each row is one combination.

Details

cross2() returns the product set of the elements of .x and .y. cross3() takes an additional .z argument. cross() takes a list .l and returns the cartesian product of all its elements in a list, with one combination by element. cross_df() is like cross() but returns a data frame, with one combination by row.

cross(), cross2() and cross3() return the cartesian product is returned in wide format. This makes it more amenable to mapping operations. cross_df() returns the output in long format just as expand.grid() does. This is adapted to rowwise operations.

When the number of combinations is large and the individual elements are heavy memory-wise, it is often useful to filter unwanted combinations on the fly with .filter. It must be a predicate function that takes the same number of arguments as the number of crossed objects (2 for cross2(), 3 for cross3(), length(.l) for cross()) and returns TRUE or FALSE. The combinations where the predicate function returns TRUE will be removed from the result.

See also

expand.grid()