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Re: Succinct way of testing array membership [message #81201]

Thu, 30 August 2012 12:16

wlandsman
Messages: 743
Registered: June 2000

Senior Member

For very large vectors, WHERE() methods are slow because (1) you compute the index of where the member is found, even if you just care about membership, and more important (2) WHERE operates on the entire vector, and does not exit as soon as the member is found. A faster method would be

function array_contains,v,x
;Is x an element of V?
return,~array_equal( (v eq x), 0b)
end

since ARRAY_EQUAL exits as soon as the first match is found. I can't imagine the speed difference is significant for normal size vectors, though.

--Wayne

On Thursday, August 30, 2012 12:51:48 PM UTC-4, godber wrote:
> Is there a more succinct way of testing array membership than using where and n_elements on the indexes? Something like array_contains(a, 'pancakes')?
>
>
>
> Austin

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[Message index]

		Re: Succinct way of testing array membership By: wlandsman on Thu, 30 August 2012 12:16
		Re: Succinct way of testing array membership By: Michael Galloy on Thu, 30 August 2012 10:09
		Re: Succinct way of testing array membership By: Russell Ryan on Thu, 30 August 2012 09:59
		Re: Succinct way of testing array membership By: DavidF[1] on Thu, 30 August 2012 09:57
		Re: Succinct way of testing array membership By: godber on Thu, 30 August 2012 13:57
		Re: Succinct way of testing array membership By: Helder Marchetto on Thu, 30 August 2012 14:12

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