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Re: Efficiently perform histogram reverse indices like procedure on a string array? [message #80994 is a reply to message #80990]

Wed, 25 July 2012 19:17

Jeremy Bailin
Messages: 618
Registered: April 2008

Senior Member

On 7/25/12 9:09 PM, Bogdanovist wrote:
> I have an array of a data structure, one tag of which is a string identifier indicating which location the data belongs to. There are many thousands of data points, but only about a dozen or so unique locations.
>
> I make frequent use of the HISTOGRAM function with the reverse_indices in order to carve up data by some identifier, most commonly the time. In this case, I want to divide out the data by site efficiently. I can't use HISTOGRAM on strings, so I need some other approach. There are plenty of ways this can be done, but I'd like some views on the better and most efficient ways to do it.
>
> Take an example, say we have a simple string array
>
> foo=['a','b','c','b','b','a','a','c']
>
> To determine the list of unique strings we could do
>
> sfoo = foo[sort(foo)]
> print,sfoo[uniq(sfoo)]
>
> We can then repeatedly use WHERE to find the indices in the data array(s) corresponding to each site.
>
> Is there a quicker/better way to do this? Repeatedly calling WHERE seems inefficient (certainly HISTOGRAM is way faster when it is usable)

Use VALUE_LOCATE to find where in the list of unique indices the
elements belong to, and use that index as a number that you can run
HISTOGRAM on.

(raise your hand everyone who saw that coming...)

-Jeremy.

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[Message index]

		Re: Efficiently perform histogram reverse indices like procedure on a string array? By: Craig Markwardt on Thu, 26 July 2012 14:33
		Re: Efficiently perform histogram reverse indices like procedure on a string array? By: Jeremy Bailin on Thu, 26 July 2012 10:41
		Re: Efficiently perform histogram reverse indices like procedure on a string array? By: ben.bighair on Thu, 26 July 2012 10:30
		Re: Efficiently perform histogram reverse indices like procedure on a string array? By: Jeremy Bailin on Wed, 25 July 2012 19:17
		Re: Efficiently perform histogram reverse indices like procedure on a string array? By: ben.bighair on Wed, 25 July 2012 18:34

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