map.md
In purrr: Functional Programming Tools

fails on non-vectors

Code
  map(environment(), identity)
Condition
  Error in `map()`:
  ! `.x` must be a vector, not an environment.

Code
  map(quote(a), identity)
Condition
  Error in `map()`:
  ! `.x` must be a vector, not a symbol.

all inform about location of problem

Code
  map_int(1:3, ~ fail_at_3(.x, 2:1))
Condition
  Error in `map_int()`:
  i In index: 3.
  Caused by error:
  ! Result must be length 1, not 2.
Code
  map_int(1:3, ~ fail_at_3(.x, "x"))
Condition
  Error in `map_int()`:
  i In index: 3.
  Caused by error:
  ! Can't coerce from a string to an integer.
Code
  map(1:3, ~ fail_at_3(.x, stop("Doesn't work")))
Condition
  Error in `map()`:
  i In index: 3.
  Caused by error in `fail_at_3()`:
  ! Doesn't work

error location uses name if present

Code
  map_int(c(a = 1, b = 2, c = 3), ~ fail_at_3(.x, stop("Error")))
Condition
  Error in `map_int()`:
  i In index: 3.
  i With name: c.
  Caused by error in `fail_at_3()`:
  ! Error
Code
  map_int(c(a = 1, b = 2, 3), ~ fail_at_3(.x, stop("Error")))
Condition
  Error in `map_int()`:
  i In index: 3.
  Caused by error in `fail_at_3()`:
  ! Error

requires output be length 1 and have common type

Code
  map_vec(1:2, ~ rep(1, .x))
Condition
  Error in `map_vec()`:
  ! `out[[2]]` must have size 1, not size 2.
Code
  map_vec(1:2, ~ if (.x == 1) factor("x") else 1)
Condition
  Error in `map_vec()`:
  ! Can't combine `<list>[[1]]` <factor<bf275>> and `<list>[[2]]` <double>.

can enforce .ptype

Code
  map_vec(1:2, ~ factor("x"), .ptype = integer())
Condition
  Error in `map_vec()`:
  ! Can't convert `<list>[[1]]` <factor<bf275>> to <integer>.