extract.md
In tidyr: Tidy Messy Data

informative error message if wrong number of groups

Code
  (expect_error(extract(df, x, "y", ".")))
Output
  <error/rlang_error>
  Error in `extract()`:
  ! `regex` should define 1 groups; 0 found.
Code
  (expect_error(extract(df, x, c("y", "z"), ".")))
Output
  <error/rlang_error>
  Error in `extract()`:
  ! `regex` should define 2 groups; 0 found.

informative error if using stringr modifier functions (#693)

Code
  (expect_error(extract(df, x, "x", regex = regex)))
Output
  <error/rlang_error>
  Error in `extract()`:
  ! `regex` can't use modifiers from stringr.

validates its inputs

Code
  df %>% extract()
Condition
  Error in `extract()`:
  ! `col` is absent but must be supplied.
Code
  df %>% extract(x, regex = 1)
Condition
  Error in `extract()`:
  ! `regex` must be a single string, not the number 1.
Code
  df %>% extract(x, into = 1:3)
Condition
  Error in `extract()`:
  ! `into` must be a character vector, not an integer vector.
Code
  df %>% extract(x, into = "x", convert = 1)
Condition
  Error in `extract()`:
  ! `convert` must be `TRUE` or `FALSE`, not the number 1.