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purrr 0.2.3

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@lionel- lionel- released this 03 Aug 07:12

Breaking changes

We noticed the following issues during reverse dependencies checks:

  • If reduce() fails with this message:

    Error: `.x` is empty, and  no `.init` supplied

    this is because reduce() now returns .init when .x is
    empty. Fix the problem by supplying an appropriate argument to
    .init, or by providing special behaviour when .x has length 0.

  • The type predicates have been migrated to rlang. Consequently the
    bare-type-predicates documentation topic is no longer in purrr,
    which might cause a warning if you cross-reference it.


purrr no longer depends on lazyeval or Rcpp (or dplyr, as of the
previous version). This makes the dependency graph of the tidyverse
simpler, and makes purrr more suitable as a dependency of lower-level

There have also been two changes to eliminate name conflicts between
purrr and dplyr:

  • order_by(), sort_by() and split_by() have been removed. order_by()
    conflicted with dplyr::order_by() and the complete family doesn't feel that
    useful. Use tibbles instead (#217).

  • contains() has been renamed to has_element() to avoid conflicts with
    dplyr (#217).


The plucking mechanism used for indexing into data structures with
map() has been extracted into the function pluck(). Plucking is
often more readable to extract an element buried in a deep data
structure. Compare this syntax-heavy extraction which reads


to the equivalent pluck:

x %>% pluck(1, accessor, "foo")

Map helpers

  • as_function() is now as_mapper() because it is a tranformation that
    makes sense primarily for mapping functions, not in general (#298).
    .null has been renamed to .default to better reflect its intent (#298).
    .default is returned whenever an element is absent or empty (#231, #254).

    as_mapper() sanitises primitive functions by transforming them to
    closures with standardised argument names (using rlang::as_closure()).
    For instance + is transformed to function(.x, .y) .x + .y. This
    results in proper argument matching so that map(1:10, partial(-, .x = 5)) produces list(5 - 1, 5 - 2, ...).

  • Recursive indexing can now extract objects out of environments (#213) and
    S4 objects (#200), as well as lists.

  • attr_getter() makes it possible to extract from attributes
    like map(list(iris, mtcars), attr_getter("row.names")).

  • The argument list for formula-functions has been tweaked so that you can
    refer to arguments by position with ..1, ..2, and so on. This makes it
    possible to use the formula shorthand for functions with more than two
    arguments (#289).

  • possibly(), safely() and friends no longer capture interrupts: this
    means that you can now terminate a mapper using one of these with
    Escape or Ctrl + C (#314)

Map functions

  • All map functions now treat NULL the same way as an empty vector (#199),
    and return an empty vector if any input is an empty vector.

  • All map() functions now force their arguments in the same way that base R
    does for lapply() (#191). This makes map() etc easier to use when
    generating functions.

  • A new family of "indexed" map functions, imap(), imap_lgl() etc,
    provide a short-hand for map2(x, names(x)) or map2(x, seq_along(x))

  • The data frame suffix _df has been (soft) deprecated in favour of
    _dfr to more clearly indicate that it's a row-bind. All variants now
    also have a _dfc for column binding (#167). (These will not be terribly
    useful until dplyr::bind_rows()/dplyr::bind_cols() have better
    semantics for vectors.)

Modify functions

A new modify() family returns the same output of the type as the
input .x. This is in contrast to the map() family which always
returns a list, regardless of the input type.

The modify functions are S3 generics. However their default methods
should be sufficient for most classes since they rely on the semantics
of [<-. modify.default() is thus a shorthand for x[] <- map(x, f).

  • at_depth() has been renamed to modify_depth().

  • modify_depth() gains new .ragged argument, and negative depths are
    now computed relative to the deepest component of the list (#236).

New functions

  • auto_browse(f) returns a new function that automatically calls browser()
    if f throws an error (#281).

  • vec_depth() computes the depth (i.e. the number of levels of indexing)
    or a vector (#243).

  • reduce2() and reduce2_right() make it possible to reduce with a
    3 argument function where the first argument is the accumulated value, the
    second argument is .x, and the third argument is .y (#163).

  • list_modify() extends stats::modifyList() to replace by position
    if the list is not named.(#201). list_merge() operates similarly
    to list_modify() but combines instead of replacing (#322).

  • The legacy function update_list() is basically a version of
    list_modify that evaluates formulas within the list. It is likely
    to be deprecated in the future in favour of a tidyeval interface
    such as a list method for dplyr::mutate().

Minor improvements and bug fixes

  • Thanks to @dchiu911, the unit test coverage of purrr is now much greater.

  • All predicate functions are re-exported from rlang (#124).

  • compact() now works with standard mapper conventions (#282).

  • cross_n() has been renamed to cross(). The _n suffix was
    removed for consistency with pmap() (originally called map_n()
    at the start of the project) and transpose() (originally called
    zip_n()). Similarly, cross_d() has been renamed to cross_df()
    for consistency with map_df().

  • every() and some() now return NA if present in the input (#174).

  • invoke() uses a more robust approach to generate the argument list (#249)
    It no longer uses lazyeval to figure out which enviroment a character f
    comes from.

  • is_numeric() and is_scalar_numeric() are deprecated because they
    don't test for what you might expect at first sight.

  • reduce() now throws an error if .x is empty and .init is not

  • Deprecated functions flatmap(), map3(), map_n(), walk3(),
    walk_n(), zip2(), zip3(), zip_n() have been removed.

  • pmap() coerces data frames to lists to avoid the expensive [.data.frame
    which provides security that is unneeded here (#220).

  • rdunif() checks its inputs for validity (#211).

  • set_names() can now take a function to tranform the names programmatically
    (#276), and you can supply names in ... to reduce typing even more
    more (#316). set_names() is now powered by rlang::set_names().

  • safely() now actually uses the quiet argument (#296).

  • transpose() now matches by name if available (#164). You can
    override the default choice with the new .names argument.

  • The function argument of detect() and detect_index() have been
    renamed from .p to .f. This is because they have mapper
    semantics rather than predicate semantics.