map2.md
In purrr: Functional Programming Tools

verifies result types and length

Code
  map2_int(1, 1, ~"x")
Condition
  Error in `map2_int()`:
  i In index: 1.
  Caused by error:
  ! Can't coerce from a string to an integer.
Code
  map2_int(1, 1, ~ 1:2)
Condition
  Error in `map2_int()`:
  i In index: 1.
  Caused by error:
  ! Result must be length 1, not 2.
Code
  map2_vec(1, 1, ~1, .ptype = character())
Condition
  Error in `map2_vec()`:
  ! Can't convert `<list>[[1]]` <double> to <character>.

requires vector inputs

Code
  map2(environment(), "a", identity)
Condition
  Error in `map2()`:
  ! `.x` must be a vector, not an environment.
Code
  map2("a", environment(), "a", identity)
Condition
  Error in `map2()`:
  ! `.y` must be a vector, not an environment.

recycles inputs

Code
  map2(1:2, 1:3, `+`)
Condition
  Error in `map2()`:
  ! Can't recycle `.x` (size 2) to match `.y` (size 3).
Code
  map2(1:2, integer(), `+`)
Condition
  Error in `map2()`:
  ! Can't recycle `.x` (size 2) to match `.y` (size 0).