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Re: Lots of files [message #53131 is a reply to message #53058]

Mon, 19 March 2007 09:41

lasse
Messages: 48
Registered: February 2007

Member

On 19 Mar, 14:31, David Fanning <n...@dfanning.com> wrote:
> David Fanning writes:
>> Use POINT_LUN, -fin, position & Print, position.
>
> Whoops! Should be:
>
> POINT_LUN, fin, -position & Print, position

no, first solution was correct, using negative file units reads
pointer location rather than setting it.

aaaanyway...

As David suspected (to be honest, I had that feeling, too), the readf
command reads from a file unit until it reaches a newline, then
formats the string according to the format code given (IDL help says:
On input, read data from the file and format it according to the
format code.). Therefore my code was slow, because it read 4MB of data
and then chucked away ... well, lots of it.

If one uses readu instead, one cannot use format code ("The READU
procedure reads unformatted binary data") but it just reads as many
bytes as fit in the variable provided. Hence

line = bytarr(1440)
openr, fin, filename, /get_lun
while not(eof(fin)) do begin
readu, fin, line
hstat = String(line[12:14])
tmp = where(stats eq hstat)
printf, tmp[0]+1, string(line)
endwhile

works like a charm, too. and please note, finally I am able to use the
not(eof(fin)) condition.

Oh, and by the way, the above program runs in 0.05 seconds, whereas
the readf with format takes 75 seconds but that doesn't surprise
anybody, I guess.

Right, that sorted, let's get some work done...
Cheers
Lasse

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[Message index]

		Lots of files By: lasse on Fri, 16 March 2007 10:36
		Re: Lots of files By: Foldy Lajos on Mon, 19 March 2007 10:01
		Re: Lots of files By: lasse on Mon, 19 March 2007 09:41
		Re: Lots of files By: David Fanning on Mon, 19 March 2007 07:31
		Re: Lots of files By: David Fanning on Mon, 19 March 2007 07:27
		Re: Lots of files By: lasse on Mon, 19 March 2007 04:32

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