From: Max Williams <toastkid.williams@...>
Date: 2007-11-13T00:14:08+09:00
Subject: Re: array select

Max Williams wrote:
> Luca Roma wrote:
>> i have 2 arrays of objects: dates and places
>> 
>> dates have attribute place_id
>> and places have id
>> 
>> I must to selezionate all places that have id in array of objects dates.
>> 
>> dates.select{|obj| obj.place_id in places[].id }
>> 
>> How i can replace "in places[].id " to works it?
>> Thanks
> 
> You could use Array#collect, which creates a new array out of another 
> array, taking a block of code that processes an element of the old array 
> and spits out something to go into the new array.
> 
> so,
>   places[].id
> 
> would be
>   places.collect{ |place| place.id}
> 
> You can then ask if obj.place_id is in this, as follows:
> 
>   dates.select{ |obj| places.collect{ |place| 
> place.id}.include?(obj.place_id) }
> 
> I think that's what you're after (i'm not exactly sure from your 
> question, sorry).

Just occurred to me that this is horribly inefficient as you remake the 
collection for each member of dates!  It would be better to make the new 
array first:

place_ids = places.collect{ |place| place.id}
dates.select{ |obj| place_ids.include?(obj.place_id) }
-- 
Posted via http://www.ruby-forum.com/.