tidyr 1.1.0

General features

• pivot_longer(), hoist(), unnest_wider(), and unnest_longer() gain
  new transform arguments; these allow you to transform values "in flight".
  They are partly needed because vctrs coercion rules have become stricter,
  but they give you greater flexibility than was available previously (#921).

• Arguments that use tidy selection syntax are now clearly documented and
  have been updated to use tidyselect 1.1.0 (#872).

Pivoting improvements

• Both pivot_wider() and pivot_longer() are considerably more performant,
  thanks largely to improvements in the underlying vctrs code
  (#790, @DavisVaughan).

• pivot_longer() now supports names_to = character() which prevents the
  name column from being created (#961).

  df <- tibble(id = 1:3, x_1 = 1:3, x_2 = 4:6)  
  df %>% pivot_longer(-id, names_to = character())
  

• pivot_longer() no longer creates a .copy variable in the presence of
  duplicate column names. This makes it more consistent with the handling
  of non-unique specs.

• pivot_longer() automatically disambiguates non-unique ouputs, which can
  occur when the input variables include some additional component that you
  don't care about and want to discard (#792, #793).

  df <- tibble(id = 1:3, x_1 = 1:3, x_2 = 4:6)  
  df %>% pivot_longer(-id, names_pattern = "(.)_.")
  df %>% pivot_longer(-id, names_sep = "_", names_to = c("name", NA))
  df %>% pivot_longer(-id, names_sep = "_", names_to = c(".value", NA))
  

• pivot_wider() gains a names_sort argument which allows you to sort
  column names in order. The default, FALSE, orders columms by their
  first appearance (#839). In a future version, I'll consider changing the
  default to TRUE.

• pivot_wider() gains a names_glue argument that allows you to construct
  output column names with a glue specification.

• pivot_wider() arguments values_fn and values_fill can now be single
  values; you now only need to use a named list if you want to use different
  values for different value columns (#739, #746). They also get improved
  errors if they're not of the expected type.

Rectangling

• hoist() now automatically names pluckers that are a single string (#837).
  It error if you use duplicated column names (@mgirlich, #834), and now uses
  rlang::list2() behind the scenes (which means that you can now use !!!
  and :=) (#801).

• unnest_longer(), unnest_wider(), and hoist() do a better job
  simplifying list-cols. They no longer add unneeded unspecified() when
  the result is still a list (#806), and work when the list contains
  non-vectors (#810, #848).

• unnest_wider(names_sep = "") now provides default names for unnamed inputs,
  suppressing the many previous name repair messages (#742).

Nesting

• pack() and nest() gains a .names_sep argument allows you to strip outer
  names from inner names, in symmetrical way to how the same argument to
  unpack() and unnest() combines inner and outer names (#795, #797).

• unnest_wider() and unnest_longer() can now unnest list_of columns. This
  is important for unnesting columns created from nest() and with
  pivot_wider(), which will create list_of columns if the id columns are
  non-unique (#741).

Bug fixes and minor improvements

• chop() now creates list-columns of class vctrs::list_of(). This helps
  keep track of the type in case the chopped data frame is empty, allowing
  unchop() to reconstitute a data frame with the correct number and types
  of column even when there are no observations.

• drop_na() now preserves attributes of unclassed vectors (#905).

• expand(), expand_grid(), crossing(), and nesting() once again
  evaluate their inputs iteratively, so you can refer to freshly created
  columns, e.g. crossing(x = seq(-2, 2), y = x) (#820).

• expand(), expand_grid(), crossing(), and nesting() gain a
  .name_repair giving you control over their name repair strategy
  (@jeffreypullin, #798).

• extract() lets you use NA in into, as documented (#793).

• extract(), separate(), hoist(), unnest_longer(), and unnest_wider()
  give a better error message if col is missing (#805).

• pack()'s first argument is now .data instead of data (#759).

• pivot_longer() now errors if values_to is not a length-1 character vector
  (#949).

• pivot_longer() and pivot_wider() are now generic so implementations
  can be provided for objects other than data frames (#800).

• pivot_wider() can now pivot data frame columns (#926)

• unite(na.rm = TRUE) now works for all types of variable, not just character
  vectors (#765).

• unnest_wider() gives a better error message if you attempt to unnest
  multiple columns (#740).

• unnest_auto() works when the input data contains a column called col
  (#959).