Feature #13777: Array#delete_all

• Status: Rejected
• Assignee: -
• Target version: -

[k0kubun (Takashi Kokubun)]

I want Array#delete_if which returns array of deleted values.

For following code,

array = ["a", "aa", "ab", "bb", "c"]
result = {}
until array.empty?
  key = array.first
  group, array = array.partition { |v| v.start_with?(key) }
  result[key] = group
end
result #=> {"a"=>["a", "aa", "ab"], "bb"=>["bb"], "c"=>["c"]}

With Array#delete_all, This would be able to be written in more elegant way like:

array = ["a", "aa", "ab", "bb", "c"]
result = {}
until array.empty?
  key = array.first
  result[key] = array.delete_all { |v| v.start_with?(key) }
end
result #=> {"a"=>["a", "aa", "ab"], "bb"=>["bb"], "c"=>["c"]}

This is simplified source code of real use case in Haml: https://github.com/haml/haml/blob/923a0d78874fe1d369f8c7a0bf77f67b2c2139bb/lib/haml/attribute_compiler.rb#L75-L76
This grouping task is necessary for Haml optimization.

Do you know simpler way to write this with existing methods?

[shevegen (Robert A. Heiler)]

I myself usually use .reject! and .select! and then apply the reverse prior to that
if I need to keep these entries as well (or respectively without the '!').

My approach also needs more lines.

If I understood it correctly so then you want to have an operation where you can
not only manipulate the variable at hand, but also additionally select the
entries that were deleted. I do not know of a better way than the one you showed
though, at the least not with any fewer lines of code.

[matz (Yukihiro Matsumoto)]

• Status changed from Open to Rejected

The name delete_all is not acceptable. This method works as a modifying version of partition. The name does not indicate the fact. This can be achieved by

result = []
ary.delete_if do|e|
  if cond(e)
    result << e
    true
  end
end

If the use-case is frequent and needs to be supported by the core, we will re-investigate. Please reopen.

Matz.