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Re: Faster way to search/split a string? [message #78450 is a reply to message #78448]

Thu, 24 November 2011 06:16

rjp23
Messages: 97
Registered: June 2010

Member

On Nov 24, 9:15 am, wlandsman <wlands...@gmail.com> wrote:
> Some thoughts (though I am not certain I understand the situation):
>
> 1. If you don't need regular expressions then I believe that using STRPOS() is quicker than using STREGEX().
> 2. If the ID is always in the first 20 characters of ALL_ROWS then I would created a new vector row_id = strmid(all_rows,0,20) and search on that.
> 3. If the ID is always exactly 20 characters, you could use a program likehttp://idlastro.gsfc.nasa.gov/ftp/pro/misc/match.proto then find the matching indices in row_id and id. This is similar to David's suggestion of sorting and using VALUE_LOCATE.
> 4. You want to make only a single call to STRSPLIT() for all 10,000 rows. Since IDL V8.0, STRSPLIT returns a list data type when supplied with an array (since in principle each string element could have a different number of "columns"). If you have an earlier version of IDL -- or if this capability is not available in GDL, then I would use the vector capability of STRMID (http://www.idlcoyote.com/code_tips/strmidvec.html)
>
> --Wayne

Thanks for that. Doing #2 made a huge difference along with David's
suggestion.

On a related note but a different problem (and I know people aren't
GDL experts here so apologies) I'm finding that strsplit in GDL is
much slower than in IDL. Has anyone come across this before? I've
tried searching the GDL help but it's obviously not as extensive as
here.

I also just wanted to check that I'm doing this the optimum way for
IDL.

If I have a string array like: array=[abc_001, abc_002, abc_003,
bcdef_001, bcdef_002, cdf_001_001, cdf_001_002]

I've assumed the fastest way to get the start section characters is to
do:

for loop=0, n_elements(array)-1 do begin
start_section[loop]=(strsplit(array[loop], '_', /extract))[0]
endfor

or is there a vectorised way to use strsplit in IDL? (limited to IDL 7
and/or GDL)

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[Message index]

		Re: Faster way to search/split a string? By: rjp23 on Thu, 24 November 2011 06:41
		Re: Faster way to search/split a string? By: rjp23 on Thu, 24 November 2011 06:16
		Re: Faster way to search/split a string? By: wlandsman on Thu, 24 November 2011 01:15
		Re: Faster way to search/split a string? By: David Fanning on Wed, 23 November 2011 10:21
		Re: Faster way to search/split a string? By: Vincent Sarago on Wed, 23 November 2011 10:17
		Re: Faster way to search/split a string? By: Jeremy Bailin on Wed, 23 November 2011 08:02
		Re: Faster way to search/split a string? By: rjp23 on Wed, 23 November 2011 07:37
		Re: Faster way to search/split a string? By: David Fanning on Wed, 23 November 2011 06:40

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