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comp.lang.ruby

Enumerable#find return index

Tod McIntyre

3/15/2006 4:08:00 AM

This is quite embarassing because I Don't consider myself a poor
programmer, but I just started looking at ruby the other day.

Blocks seem to be a good way to iterate through something to search for
an entry for instance. It's easy to return the object that meets
certain criteria using blocks but I'm finding it hard to return the
index of that particular object in, say, an array.

as an example

arr=[4,1,3,7]
arr.find { |f| f==someval }
will return the val within arr that matches someval, which doesn't
really help me because I already have someval

How do I actually return the index in arr to the first match of someval.

so if someval == 3, my block would return 2, for the above example


--
Posted via http://www.ruby-....
7 Answers

Daniel Baird

3/15/2006 4:15:00 AM

0

try
arr.index(3)

;Daniel

On 15/03/06, Tod McIntyre <todmcintyre@gmail.com> wrote:
>
> This is quite embarassing because I Don't consider myself a poor
> programmer, but I just started looking at ruby the other day.
>
> Blocks seem to be a good way to iterate through something to search for
> an entry for instance. It's easy to return the object that meets
> certain criteria using blocks but I'm finding it hard to return the
> index of that particular object in, say, an array.
>
> as an example
>
> arr=[4,1,3,7]
> arr.find { |f| f==someval }
> will return the val within arr that matches someval, which doesn't
> really help me because I already have someval
>
> How do I actually return the index in arr to the first match of someval.
>
> so if someval == 3, my block would return 2, for the above example
>
>
> --
> Posted via http://www.ruby-....
>
>


--
Daniel Baird
http://danie... (TiddlyW;nks! :: Whiteboard Koala :: Blog :: Things
That Suck)
[[My webhost uptime is ~ 92%.. if no answer pls call again later!]]

Ross Bamford

3/15/2006 8:21:00 AM

0

On Wed, 2006-03-15 at 13:08 +0900, Tod McIntyre wrote:
> This is quite embarassing because I Don't consider myself a poor
> programmer, but I just started looking at ruby the other day.
>
> Blocks seem to be a good way to iterate through something to search for
> an entry for instance. It's easy to return the object that meets
> certain criteria using blocks but I'm finding it hard to return the
> index of that particular object in, say, an array.

Check out this thread:

http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-t...

(The upshot is that in CVS, 1.9 now allows a block to #index to specify
what is to be found).

In the meantime, the current #index should do the job for most cases
(e.g. the example you showed):

a = [:a,:b,:c,:d,:e]
# => [:a, :b, :c, :d, :e]

a.index(:a)
# => 0

a.index(:e)
# => 4

--
Ross Bamford - rosco@roscopeco.REMOVE.co.uk

Robert Klemme

3/15/2006 2:21:00 PM

0


"Tod McIntyre" <todmcintyre@gmail.com> wrote in message
news:da9c35364b80a5c4e9e603e0db41190a@ruby-forum.com...
> This is quite embarassing because I Don't consider myself a poor
> programmer, but I just started looking at ruby the other day.
>
> Blocks seem to be a good way to iterate through something to search for
> an entry for instance. It's easy to return the object that meets
> certain criteria using blocks but I'm finding it hard to return the
> index of that particular object in, say, an array.
>
> as an example
>
> arr=[4,1,3,7]
> arr.find { |f| f==someval }
> will return the val within arr that matches someval, which doesn't
> really help me because I already have someval

Yeah, but this is just a special case. With a block you can employ
arbitrary selection criteria - not just ==.

> How do I actually return the index in arr to the first match of someval.
>
> so if someval == 3, my block would return 2, for the above example

As Ross and Daniel have pointed out already, use #index.

Kind regards

robert

Tod McIntyre

3/15/2006 3:39:00 PM

0

Robert Klemme wrote:
> "Tod McIntyre" <todmcintyre@gmail.com> wrote in message
> news:da9c35364b80a5c4e9e603e0db41190a@ruby-forum.com...
>> arr=[4,1,3,7]
>> arr.find { |f| f==someval }
>> will return the val within arr that matches someval, which doesn't
>> really help me because I already have someval
>
> Yeah, but this is just a special case. With a block you can employ
> arbitrary selection criteria - not just ==.
>
>> How do I actually return the index in arr to the first match of someval.
>>
>> so if someval == 3, my block would return 2, for the above example
>
> As Ross and Daniel have pointed out already, use #index.
>
> Kind regards
>
> robert

Once again I knew this would be a simple answer!! I thank you for your
quick responses. Obviously I should be reading the api more thoroughly
before posting.

--
Posted via http://www.ruby-....

Robert Klemme

3/15/2006 3:49:00 PM

0


"Tod McIntyre" <todmcintyre@gmail.com> wrote in message
news:859233703646963b97fe343fb84b6e0f@ruby-forum.com...
> Robert Klemme wrote:
>> "Tod McIntyre" <todmcintyre@gmail.com> wrote in message
>> news:da9c35364b80a5c4e9e603e0db41190a@ruby-forum.com...
>>> arr=[4,1,3,7]
>>> arr.find { |f| f==someval }
>>> will return the val within arr that matches someval, which doesn't
>>> really help me because I already have someval
>>
>> Yeah, but this is just a special case. With a block you can employ
>> arbitrary selection criteria - not just ==.
>>
>>> How do I actually return the index in arr to the first match of
>>> someval.
>>>
>>> so if someval == 3, my block would return 2, for the above example
>>
>> As Ross and Daniel have pointed out already, use #index.
>>
>> Kind regards
>>
>> robert
>
> Once again I knew this would be a simple answer!! I thank you for your
> quick responses. Obviously I should be reading the api more thoroughly
> before posting.

Ah, don't bother. The API of the standard lib has it's humps and bumps
(for example not fully consistent usage of ! for destructive methods etc.)
so it's normal to fall into one or the other pit initially.

Kind regards

robert

dblack

3/15/2006 4:26:00 PM

0

Robert Klemme

3/15/2006 4:41:00 PM

0


<dblack@wobblini.net> wrote in message
news:Pine.LNX.4.64.0603150822080.17960@wobblini.net...
> Hi --
>
> On Thu, 16 Mar 2006, Robert Klemme wrote:
>
>> Ah, don't bother. The API of the standard lib has it's humps and bumps
>> (for example not fully consistent usage of ! for destructive methods
>> etc.) so it's normal to fall into one or the other pit initially.
>
> I have to leap to the defense of ! :-) It really is consistent:
>
> * given meth and meth!, meth! is the more "dangerous" version
> * "dangerous" often means "receiver-changing", but definitely
> does not have to mean that

Although it's certainly the most common use of "!".

> * methods whose names already imply receiver-changing don't
> have a ! because they don't need one, and also ! methods
> only come in pairs with a non-! equivalent. (It would be
> hard to imagine what "Replace the contents of this string
> object, but without changing the object" would mean....)
>
> "Implying receiver-changing" is of course in the eyes of Matz :-) But
> while there are judgements, I don't think there's any inconsistency.

Um, yes. I should print this out and place it in front of my monitor.
Somehow I keep forgetting this definition - must be some old newsgroup
thread having anchored deep in my subconscious.

Thanks for putting that straight!

Kind regards

robert