comp.lang.idl-pvwave archive: archive » Re: Efficiently perform histogram reverse indices like procedure on a string array?

Home » Public Forums » archive » Re: Efficiently perform histogram reverse indices like procedure on a string array?

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: Efficiently perform histogram reverse indices like procedure on a string array? [message #80995 is a reply to message #80994]

Wed, 25 July 2012 18:34

ben.bighair
Messages: 221
Registered: April 2007

Senior Member

On Wednesday, July 25, 2012 7:39:33 PM UTC-4, 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& #39;,'b','b','a& #39;,'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)

Hi,

You can convert your strings to unique numbers - it's a bit awkward - and then you may find the the spacing between populated bins makes the whole thing drag when you do the histogram. But here goes...

foo = ['az','bs','cd','ba','ba','az','aa','c'] ; tricky strings
boo = strtrim(fix(byte(foo)),2) ; note the 'fix' in there
soo = strjoin(boo)
noo = long(soo)

There you go - numbers as unique as the strings you started with.

Cheers,
Ben

Report message to a moderator

[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

Previous Topic:	Is this a legitimate way of projection and subset?
Next Topic:	cgcontour not outputting?

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Fri Oct 10 10:01:13 PDT 2025

Total time taken to generate the page: 1.43929 seconds