Comparisons in purrr

[lionel-]

reduce_common <- function(x, msg = "Objects must be identical",
                          operator = identical) {
  reduce(x, function(.x, .y) {
    if (!operator(.x, .y)) {
      stop(msg, call. = FALSE)
    }
    .y
  })
}

reduce_common_lgl <- function(.x, operator = identical) {
  safe_reduce_common <- safely(reduce_common)
  reduced <- safe_reduce_common(.x, operator = operator)
  is.null(reduced$error)
}

#' Companion to identical()
equal <- function(x, y) {
  isTRUE(all.equal(x, y))
}

all_equal <- function(x) {
  reduce_common_lgl(x, operator = equal)
}
all_identical <- function(x) {
  reduce_common_lgl(x)
}

list(1, 1, 1.0001) %>% all_equal()
#> [1] FALSE

list(1, 1, 1.00000000001) %>% all_equal()
#> [1] TRUE

list(1, 1, 1.00000000001) %>% all_identical()
#> [1] FALSE

[lionel-]

From a stylistic point of view, I'm not sure if it's better to use a functional + error throwing, rather than a for loop + break.

In the latter case we'd have the loop inside reduce_common_lgl() called by the user-facing reduce_common() which would throw an error on FALSE.

[lionel-]

Maybe the stylistic rule should be that when we break the purity of (part of) a function we shouldn't apply a functional makeup on it. In that case the for loop is better (and more efficient).

[hadley]

Can you move that to vctrs?

[lionel-]

Moved to rlang