Hash#select and Hash#map return arrays. In some cases I want to get
hashes back instead.
I can take the returned arrays and transform them back into hashes,
but it would be nice to avoid the extra step.
Plus, it just surprised me that #select and #map aren't overridden for
Hash to return new Hashes instead of arrays.
Am I missing something?
Jeff
# use two vars in an map/select block (or use the index if one var)
array = {:a => 1, :b =>2}.select {|k,v| k == :b}
# => [[:b, 2]]
# use inject to make a hash from a list, this is a great technique
hash = array.inject({}) {|h,e| h.merge({e[0] => e[1]}) }
# => {:b=>2}
-franco
On Sep 17, 6:05 pm, Jeff <cohen.j...@gmail.com> wrote:
Hash#select and Hash#map return arrays. In some cases I want to get
hashes back instead.I can take the returned arrays and transform them back into hashes,
but it would be nice to avoid the extra step.Plus, it just surprised me that #select and #map aren't overridden for
Hash to return new Hashes instead of arrays.Am I missing something?
Jeff
# I can take the returned arrays and transform them back into hashes,
# but it would be nice to avoid the extra step.
# Plus, it just surprised me that #select and #map aren't overridden for
# Hash to return new Hashes instead of arrays.
# Am I missing something?
none. just wait for 1.9 http://eigenclass.org/hiki.rb?Changes+in+Ruby+1.9#l81
i think this is an faq. in this regard, i'd like to request that the ruby faq be on the frontpage of ruby-lang.org and ruby-doc.org and that it be mirrored.
kind regards -botp
From: Jeff [mailto:cohen.jeff@gmail.com]
That was exactly my point - why doesn't Hash#select and Hash#map
return hashes instead of arrays?
Jeff
On Sep 17, 8:35 pm, franco <flazzar...@gmail.com> wrote:
# use two vars in an map/select block (or use the index if one var)
array = {:a => 1, :b =>2}.select {|k,v| k == :b}
# => [[:b, 2]]# use inject to make a hash from a list, this is a great technique
hash = array.inject({}) {|h,e| h.merge({e[0] => e[1]}) }
# => {:b=>2}-franco
Thanks for the info.
Jeff
On Sep 17, 11:45 pm, Peña, Botp <b...@delmonte-phil.com> wrote:
From: Jeff [mailto:cohen.j...@gmail.com]
just wait for 1.9http://eigenclass.org/hiki.rb?Changes+in+Ruby+1.9#l81
Hi Jeff.
My guess is because you need to enumerate over a Hash. Recall that entries
in a Hash are indexed by some Hashing algorithm, so it's kind of had to
enumerate over it's entries.
It's probably cheaper to toss all the entries in a Hash into an array and
iterate over it's index than to try and divine some means of iterating over
the non-sequential Hash table containing index values.
James
On 9/17/07, Jeff <cohen.jeff@gmail.com> wrote:
On Sep 17, 8:35 pm, franco <flazzar...@gmail.com> wrote:
> # use two vars in an map/select block (or use the index if one var)
> array = {:a => 1, :b =>2}.select {|k,v| k == :b}
> # => [[:b, 2]]
>
> # use inject to make a hash from a list, this is a great technique
> hash = array.inject({}) {|h,e| h.merge({e[0] => e[1]}) }
> # => {:b=>2}
>
> -francoThat was exactly my point - why doesn't Hash#select and Hash#map
return hashes instead of arrays?Jeff
Hey Jeff.
You're in luck! This morning an article was posted to "Softies on Rails" on
how to override select to get back a Hash:
http://www.softiesonrails.com/2007/9/18/ruby-201-weird-hash-syntax
James
On 9/18/07, Jeff <cohen.jeff@gmail.com> wrote:
On Sep 17, 11:45 pm, Peña, Botp <b...@delmonte-phil.com> wrote:
> From: Jeff [mailto:cohen.j...@gmail.com]
> just wait for 1.9http://eigenclass.org/hiki.rb?Changes+in+Ruby+1.9#l81Thanks for the info.
Jeff
With some changes to undo top-posting:
> why doesn't Hash#select and Hash#map
> return hashes instead of arrays?
My guess is because you need to enumerate over a Hash. Recall that entries
in a Hash are indexed by some Hashing algorithm, so it's kind of had to
enumerate over it's entries.
There's no problem enumerating over a Hash. Hash#each is implemented
after all. Enumerable only requires that each yield all of the
elements in SOME order, the fact that Hashes don't have a natural
ordering doesn't hamper this. Hash#each yields key,value pairs.
Ruby 1.9 is on track to change Hash#select to return a Hash.
Hash#map is problematic though, map returns a new enumeration which
contains the elements resulting in applying the block to each element
yielded by each. In general this could be anything for example:
{:a => "fred", :b => "barney"}.map { |k,v| "#{k} is associated
with #{v}" } # => ["a is associated with fred", "b is associated with
barney"]
On 9/18/07, James Herdman <james.herdman@gmail.com> wrote:
On 9/17/07, Jeff <cohen.jeff@gmail.com> wrote:
--
Rick DeNatale
My blog on Ruby
http://talklikeaduck.denhaven2.com/