cross_df_safe: Safely cross lists

In MiguelRodo/reportutils: Utility functions for writing reports

Safely cross lists

Description

Returns the cartesian of all its elements in a list as a dataframe, with one combination per row.

Usage

cross_df_safe(.l, .filter = NULL)

Arguments

.l	A list of lists or atomic vectors (or, a dataframe).
.filter	function. A predicate function that takes the same number of arguments as the number of variables to be combined.

Details

Elements in the list to be crossed such as list(1, 2:3) keep their multi-length elements in one combination (i.e. one dataframe row). That is the sense in which is "safe", as it behaves as expected. The function 'purrr::cross' returns an error in this case, whilst 'purrr::cross' piped 'purrr::map_df(tibble::as_tibble)' w creates two combinations (two dataframe rows) from the second list element above. One could wrap the second element in a list, but that adds an extra layer when accessing the element in the combination.

See examples for a demonstration.

Value

A dataframe with the same number of rows as

Examples

to_cross_list <- list(
 v1 = c("a", "b"),
 v2 = list(3, 4:5)
)
# returns an error
try(purrr::cross_df(to_cross_list))
# can avoid this by wrapping each to-cross
# element's elements in lists,
# but then the crossed dataframe
# has second column's elements
# each be lists
 to_cross_list_list <- list(
  v1 = c("a", "b"),
  v2 = list(list(3), list(4:5))
)
purrr::cross_df(to_cross_list_list)
# returns a four-row dataframe, where
# second column has elements of lengths 1, 1, 2 and 2
# that are not lists
cross_df_safe(to_cross_list)
# the above is more natural to work with
# no element in a combination
# is needlessly wrapped inside a list of length 1

MiguelRodo/reportutils documentation built on April 11, 2022, 3:32 p.m.