Ruby Code Snippet: Array.count

[Ian Macdonald]

On Sat 05 Jul 2003 at 08:01:38 +0900, Stefan Arentz wrote:

>
> Maybe this functionality is already somewhere in Ruby, but I could not
> find it. This little snippet extends Array with a count method. It takes
> a code block that can be used to count elements that match a specific
> condition:
>
> a = Array[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
> puts a.count { |v| v < 5 }

This is already available with Enumerable#find_all:

a = (1..10).to_a
puts a.find_all {|v| v < 5 }.size

4

Ian
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[Stefan Arentz]

Ian Macdonald <ian@caliban.org> writes:

> On Sat 05 Jul 2003 at 08:01:38 +0900, Stefan Arentz wrote:
>

> >
> > Maybe this functionality is already somewhere in Ruby, but I could not
> > find it. This little snippet extends Array with a count method. It takes
> > a code block that can be used to count elements that match a specific
> > condition:
> >
> > a = Array[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
> > puts a.count { |v| v < 5 }

>
> This is already available with Enumerable#find_all:
>
> a = (1..10).to_a
> puts a.find_all {|v| v < 5 }.size
>
> 4

Yes but this is very inefficient if you have large collections. My version
does not need to create a new temporary collection just to count it.

S.

[Dave Thomas]

Stefan Arentz wrote:

> Maybe this functionality is already somewhere in Ruby, but I could not
> find it. This little snippet extends Array with a count method. It takes
> a code block that can be used to count elements that match a specific
> condition:
>
> a = Array[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
> puts a.count { |v| v < 5 }
>
> ==> 4
>
> The code:
>
> class Array
> def count(&action)
> count = 0
> self.each { |v| count = count + 1 if action.call(v) }
> return count
> end
> end

I'm starting to like using 'inject' for this kind of thing, but it isn't
as clear to read:

class Array
def count
inject(0) {|sum, e| yield(e) ? sum + 1 : sum }
end
end

> Ruby is sweet :-)

Agreed


Cheers


Dave

[Simon Strandgaard]

On Sat, 05 Jul 2003 14:20:35 +0900, Dave Thomas wrote:

>
> class Array
> def count
> inject(0) {|sum, e| yield(e) ? sum + 1 : sum }
> end
> end

I have added your Array#count (using inject), here:

[url]http://www.rubygarden.org/ruby?StandardClassExtensions/Array[/url]

--
Simon Strandgaard

[Mauricio Fernández]

On Sat, Jul 05, 2003 at 03:43:00PM +0900, Simon Strandgaard wrote:

> On Sat, 05 Jul 2003 14:20:35 +0900, Dave Thomas wrote:

> >
> > class Array
> > def count
> > inject(0) {|sum, e| yield(e) ? sum + 1 : sum }
> > end
> > end

>
>
> I have added your Array#count (using inject), here:
>
> [url]http://www.rubygarden.org/ruby?StandardClassExtensions/Array[/url]

The other version is faster IMHO, and in this case at least as readable:

class Array
def count
sum = 0
each { |x| sum += 1 if yield x }
sum
end
end



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[Dave Thomas]

Simon Strandgaard wrote:

> On Sat, 05 Jul 2003 14:20:35 +0900, Dave Thomas wrote:
>

>> class Array
>> def count
>> inject(0) {|sum, e| yield(e) ? sum + 1 : sum }
>> end
>> end

>
>
>
> I have added your Array#count (using inject), here:

My code was written in response to the OP's. However, if you're going to
save it for posterity, you should really put it under Enumerable.



Dave

[Dave Thomas]

Mauricio Fernández wrote:

> The other version is faster IMHO, and in this case at least as readable:

Agreed (in fact I believe I said the original version was more
readable). I just wanted to post an alternative to start introducing
#inject...

Cheers


Dave

[Mike Stok]

In article <be61dp$j6g$03$1@news.t-online.com>,
Volker Grabsch <volker_grabsch@v.notjusthosting.com> wrote:

>Injects are *never* clear to read, are they?

Once you assimilate the idiom they aren't too bad. Readability only
"happens" when a reader looks at something, I don't think it's an
inherent property of the material being read.

Mike

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