| Re: Suppress return with readf ? [message #13405] |
Wed, 04 November 1998 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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John Kwiatkowski (johnmk@shell.clark.net) writes:
> I have an ASCII data set that is giving me problems. I need to suppress
> the return when using readf since I only want to read in part of the
> line. Depending on the value of one of the fields there may be more
> info to read on that line. Anyone know how to stop readf from moving
> to the next line?
>
> Here is an example of 2 lines in the data file
> 0 58 2 94 2 0 0 0 0
> 0 57 7 85 44 0 0 0 2 0 0 0 2 0 0 0
>
> The first line has the 9 fields that are on every line. Depending on the
> value of the 9th field there may be 7 more fields to read on that line.
>
> psuedo code:
> A ; structure with required 9 fields
> B ; structure with optional 7 fields
>
> readf, unit, A
> if (A.field9 neq 0) then
> readf, unit B
>
> After the first read the file pointer gets placed at the next line in
> the file. How do I suppress this?
Ooohh, good question, John! I'm gonna come out of retirement
to have a go at this one. :-)
Suppose you have a data set that looks like this:
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15
You want to read the first five values on the line, and
if the last value read is "5", read 5 more values.
You certainly can't do it like this:
firstfive = IntArr(5)
nextfive = IntArr(5)
OpenR, lun, 'example.dat', /Get_Lun
ReadF, lun, firstfive
IF firstfive[4] EQ 5 THEN ReadF, lun, nextfive
Print, firstfive, nextfive
Because, as you have noticed the file pointer starts
on the next line when you do the second read. A FORMAT
keyword doesn't help either, I'm afraid (although I
*always* get in trouble when I open my mouth about
format statements.)
What you have to do instead is read the whole line
into a STRING variable, and then read the actual
values out of that string with the READS command.
Your code might look like this:
firstfive = IntArr(5)
nextfive = IntArr(5)
line = ''
OpenR, lun, 'example.dat', /Get_Lun
ReadF, lun, line
ReadS, line, firstfive
IF firstfive[4] EQ 5 THEN ReadS, line, firstfive, nextfive
Print, firstfive, nextfive
Ah, it feels good to be back in the saddle again. :-)
Cheers,
David
----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438, Toll-Free Book Orders: 1-888-461-0155
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Note: A copy of this article was e-mailed to the original poster.
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