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Re: Problem to read some data. [message #68434 is a reply to message #68420]

Mon, 26 October 2009 04:56

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

jkeller writes:

> Just use the quoted code above. This should read the data into
> variable 'a'. It will be as fast as it could be when reading text
> files with IDL.

Well, not necessarily. READ_ASCII *does*, necessarily,
use a FOR loop. If the data were all numerical (no strings),
or regularly spaced (so you could use a FORMAT statement),
then it would be much faster to allocate an array of floats
(or whatever) and read the data all at once in the IDL way.

Of course, if you don't know the number of columns and rows,
then you have to allocate time to find those things out.
For example, File_Lines has to read the entire file to count
the number of EOL markers in the file to determine how
many rows there are. But, still, even with this overhead
it is often (almost always?) faster to read data the IDL
way than to use READ_ASCII. That is the main reason I've
never used it. Even taking into account the five lines
of code you need to type, doing so was faster than waiting
for READ_ASCII to finish!

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		Re: Problem to read some data. By: d.poreh on Wed, 28 October 2009 01:25
		Re: Problem to read some data. By: jkeller on Tue, 27 October 2009 01:35
		Re: Problem to read some data. By: David Fanning on Mon, 26 October 2009 04:56
		Re: Problem to read some data. By: d.poreh on Mon, 26 October 2009 02:47
		Re: Problem to read some data. By: jkeller on Mon, 26 October 2009 00:44
		Re: Problem to read some data. By: d.poreh on Mon, 26 October 2009 00:02
		Re: Problem to read some data. By: penteado on Fri, 23 October 2009 07:01
		Re: Problem to read some data. By: d.poreh on Fri, 23 October 2009 02:42
		Re: Problem to read some data. By: pfp on Fri, 23 October 2009 02:26

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