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comp.lang.ruby

sorting an array of hash

unbewusst.sein

2/15/2007 12:15:00 PM

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
6 Answers

Farrel Lifson

2/15/2007 12:37:00 PM

0

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
>
>

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

Farrel

unbewusst.sein

2/15/2007 12:41:00 PM

0

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

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

i did that that way :

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

it's working very well ;-)


--
Une Bévue

unbewusst.sein

2/15/2007 12:46:00 PM

0

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

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

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.

--
Une Bévue

Erik Veenstra

2/15/2007 1:07:00 PM

0

> 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.erikve...

Erik Veenstra

2/15/2007 1:36:00 PM

0

> mime_types.sort!{|mime_type1,mime_type2|
> mime_type1['type'] <=> mime_type2['type']
> }
>
> it's working very well ;-)

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.erikve...

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

$ 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)

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

unbewusst.sein

2/15/2007 1:57:00 PM

0

Erik Veenstra <erikveen@gmail.com> wrote:

> 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.erikve...

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