From: Peter Vandenabeele <peter@...>
Date: 2011-10-12T02:58:26+09:00
Subject: Re: array of hashes

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On Tue, Oct 11, 2011 at 7:44 PM, botp <botpena@gmail.com> wrote:

> On Wed, Oct 12, 2011 at 1:07 AM, Mario Ruiz <tcblues@gmail.com> wrote:
> > and I would like to get a value of the array knowing the :name by doing
>
> a.find{|x| x[:name]=="pedro"}[:value]
> #=> "lsss"
>

I tried this also, but stopped when I figured out that if there is no
match for the name, this will cause an exception... I did not
see an elegant solution for that case, with the data structure
that the OP proposes.

$ irb
001:0> a = [{:name => "pedro", :value => "Isss"}]
=> [{:name=>"pedro", :value=>"Isss"}]
002:0> a.find{|x| x[:name]=="pedro"}[:value]
=> "Isss"
003:0> a.find{|x| x[:name]=="mario"}[:value]
NoMethodError: undefined method `[]' for nil:NilClass
from (irb):3
from /home/peterv/.rvm/rubies/ruby-1.9.2-p290/bin/irb:16:in `<main>'



>
> but why not directly use a hash, eg,
>
> h={}
> #=> {}
> h["mario"]="xxx"
> #=> "xxx"
> h["pedro"]="lsss"
> #=> "lsss"
>
> h["pedro"]
> #=> "lsss"
>

I agree.

A general question I have is: are there hashes or arrays in Ruby
that offer a logarithmic look-up cost (e.g. implemented with a
btree, like an indexed column on a database). That would make
it really useful to make a better implementation (like you propose)
where you can look-up directly, based on the :name.

Thx,

Peter

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