From: Robert Klemme <shortcutter@...>
Date: 2010-04-08T01:39:01+09:00
Subject: Re: Manipulating an Array of Structs

2010/4/7 Anthony Wright <anthony@overnetdata.com>:
> I have data that I've extracted from a database, that I wish to pass to
> a calling (external) piece of software through Drb.
>
> The are a large number of data set formats, but an employee based
> example might look something like:
>
> ID     Name                 Age
>  1     Mary Smith           23
>  3     Frank Zappa          52
> 19     Mary Jones           41
>
> I'm trying to find a "nice" structure to pass this data around in, so
> that it can be easily understood and manipulated.
>
> I'm currently using an Array of Hashes so it looks something like:
> [
>        { :id => 1, :name => "Mary Smith",  :age => 23 },
>        { :id => 3, :name => "Frank Zappa", :age => 52 },
>        { :id =>19, :name => "Mary Jones",  :age => 41 }
> ]
>
>
> This is fine if I want to extract single pieces of information, but it's
> clumsy to manipulate the whole array, for example, extract out all the
> names, sort the array by age, create a new array containing employees
> over 40. It's also inefficient as I'm repeating the labels on every record.
>
> I realise I can do this by writing block code to process the array, but
> I feel there must be a cleaner way to store and manipulate data of this
> form in ruby.  Something on the lines of Struct would be great to remove
> the excessing labels, but Struct doesn't help with the array manipulation.

I don't see your issue with the "array manipulation".  Fact is, that
if you have a collection of items you have to either iterate through
all to process and filter them or you need to create indexes which you
need to keep in sync with the base data (much the same way a RDBMS
does btw.).

We have Enumerable#map, #select, #reject and a few more methods which
work pretty well.  If you use Struct or OpenStruct you can even use
map like this:

all_names = employees.map(&:name)

If find that succinct enough.  And even with Hashes you get

all_names = employees.map {|emp| emp[:name]}

This is a bit more verbose but still not too way off I'd say.  My 0.02EUR.

Kind regards

robert

-- 
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