Sorting an array of hash

ruby-talk
1

i do have an array of hashes like that :

{type => aType, description => aDescription, extension => aExtension}

i'd like to sort this array by hash['type'], how to do that ?

this array represent the MIME Types.

···

--
Une Bévue

2

arrayOfHashes.sort_by{|hash| hash['type']}

Farrel

···

On 15/02/07, Une Bévue <unbewusst.sein@google.com.invalid> wrote:

i do have an array of hashes like that :

{type => aType, description => aDescription, extension => aExtension}

i'd like to sort this array by hash['type'], how to do that ?

this array represent the MIME Types.

--
Une Bévue

3

i did that that way :

mime_types.sort!{|mime_type1,mime_type2|
  mime_type1['type'] <=> mime_type2['type']
}

it's working very well :wink:

···

Une Bévue <unbewusst.sein@google.com.invalid> wrote:

i'd like to sort this array by hash['type'], how to do that ?

--
Une Bévue

4

fine thanks i did it that way :

arr.sort!{|a1,a2| a1['type'] <=> a2['type']}

is arrayOfHashes a special object in ruby ???

i didn't found #sort_by in the pikaxe pages for Array.

···

Farrel Lifson <farrel.lifson@gmail.com> wrote:

arrayOfHashes.sort_by{|hash| hash['type']}

--
Une Bévue

5

mime_types.sort!{|mime_type1,mime_type2|
   mime_type1['type'] <=> mime_type2['type']
}

it's working very well :wink:

But it's inefficient... (See benchmark below.)

You're doing a lookup in both hashes in order to compare the
types. A more efficient technique is to cache theses types.

Sort_by constructs a temporary array, where each element is an
array containing the type along with the mime type. Sort_by
than sorts this array, and extracts the mime type from the
result.

gegroet,
Erik V. - http://www.erikveen.dds.nl/

···

----------------------------------------------------------------

$ cat test.rb
require "benchmark"

array =
(1..100_000).collect do
   {:thing => rand}
end

Benchmark.bmbm do |bm|
   bm.report("sort") do
     10.times do
       array.sort do |h1, h2|
         h1[:thing] <=> h2[:thing]
       end
     end
   end

   bm.report("sort_by") do
     10.times do
       array.sort_by do |h|
         h[:thing]
       end
     end
   end
end

----------------------------------------------------------------

$ ruby test.rb
Rehearsal -------------------------------------------
sort 76.360000 0.000000 76.360000 ( 76.510000)
sort_by 7.391000 0.000000 7.391000 ( 7.391000)
--------------------------------- total: 83.751000sec

               user system total real
sort 46.967000 0.000000 46.967000 ( 47.047000)
sort_by 7.191000 0.000000 7.191000 ( 7.190000)

----------------------------------------------------------------

6

is arrayOfHashes a special object in ruby ???

arrayOfHashes is your array of hashes. You're calling it arr
and mime_types; he's calling it arrayOfHashes.

i didn't found #sort_by in the pikaxe pages for Array.

sort_by is defined in the module Enumerable. This module is
included (mixed-in?...) in Array.

gegroet,
Erik V. - http://www.erikveen.dds.nl/

7

But it's inefficient... (See benchmark below.)

it was a "one time running" script then...

You're doing a lookup in both hashes in order to compare the
types. A more efficient technique is to cache theses types.

Sort_by constructs a temporary array, where each element is an
array containing the type along with the mime type. Sort_by
than sorts this array, and extracts the mime type from the
result.

Ok i see.

gegroet,
Erik V. - http://www.erikveen.dds.nl/

Anyway, thanks a lot i've learned something today )))

···

Erik Veenstra <erikveen@gmail.com> wrote:
--
Une Bévue