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search routine [message #54247]

Fri, 01 June 2007 03:47

Laurens
Messages: 41
Registered: May 2006

Member

Hi folks,

From Martin Schultz (posted in 1999) I found the following array-search
algorithm which seems to do a fine job.
Except that i'm not able to catch the first element in the array.

Example:

Array = [0,80,100,120,180,300]
result = search, Array, 4.53

It should return index 0, if I understand it correctly, but it returns 1
instead. Now I don't quite follow the logic of the function, so maybe
someone for which it's easy to see can help me in the right direction?

> function search,data,value
>
> ; search first occurence of value in data set
> ; data must be sorted
>
> ; simple error checking on data and value
> if (n_elements(value) eq 0) then begin
> message,'Must supply sorted data array and value),/CONT
> return
> endif
>
> ndat = n_elements(data)
>
> try = fix(0.5*ndat)
> step = 0.5*try
>
> ; find index of nearest points
> while (step gt 1) do begin
> if (data[try] gt value) then $
> try = try-step $
> else $
> try = try+step
> step = fix(0.5*(step+1))
> endwhile
>
> ; now get the data point closest to value
> ; can only be one out of three (try-1, try, try+1)
> dummy = min( abs(value-data[try-1:try+1]), location )
>
> return,try+location-1
>
> end

Thnx! Laurens

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[Message index]

		search routine By: Laurens on Fri, 01 June 2007 03:47
		Re: search routine By: Paolo Grigis on Fri, 01 June 2007 08:39
		Re: search routine By: Laurens on Fri, 01 June 2007 08:24
		Re: search routine By: cmancone on Fri, 01 June 2007 07:58

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