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Re: Reading files with unknown amount of data [message #1463 is a reply to message #1358]

Thu, 30 September 1993 16:38

sterne
Messages: 15
Registered: March 1992

Junior Member

>>>> > "Robert" == Robert Davis <rdavis@aerospace.aero.org> writes:

Robert> I am trying to read a data file containing an unknown amount of
Robert> data into arrays in IDL. I know the format of the data in the
Robert> file, but not the number of pieces of data in the file.
Robert> Currently, I read the file twice; once to determine the amount
Robert> of data in the file and then a second time to actually read the
Robert> data into an array (now that I know the size of array needed).
Robert> Is there a better way to do this (without having to read the
Robert> file twice)?

Here are a couple more variations on the theme:

1. Check the size of the file on the system. In unix, if your file
is a simple formatted file, you can use the IDL command spawn:

spawn,'wc -l'+filename, result

and result will contain the number of lines in the file.

For a binary with fixed record length, you could read the size of
the file in bytes and work out the number of records from that.

2. Building on Joseph Zawodny's suggestion of using the EOF function:
sometimes you want to keep all the data around and manipulate stuff
after you have read it all in. You can use a variation like this:

a = fltarr(n,50) ; or whatever is appropriate.
; Initial guess of 50 records in the file.
openr,1,filename

count = 0

while not eof(1) do begin

if count eq (size(a))(2) then a = [[a],[a]] ; double size
; of 2nd index
readf,1,a(*,count)

count = count + 1

endwhile

close,1

a = a(*,0:ncount-1) ; trim to correct size

I've used both methods in the past, but, assuming I have control over
the software generating the numbers, I now much prefer to change the
software to make it write the number and format of the records at the
top of the file.

Hope this helps,
Phil
--
------------------------------------------------------------ ---------
Philip Sterne | sterne@dublin.llnl.gov
Lawrence Livermore National Laboratory | Phone (510) 422-2510
Livermore, CA 94550 | Fax (510) 422-7300

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[Message index]

		Re: Reading files with unknown amount of data By: pendleton on Thu, 04 November 1993 09:46
		Re: Reading files with unknown amount of data By: alans on Thu, 04 November 1993 08:09
		Re: Reading files with unknown amount of data By: zawodny on Thu, 04 November 1993 04:44
		Re: Reading files with unknown amount of data By: brau1231 on Thu, 04 November 1993 03:12
		Re: Reading files with unknown amount of data By: sterne on Thu, 30 September 1993 16:38
		Re: Reading files with unknown amount of data By: zawodny on Thu, 30 September 1993 12:27
		Re: Reading files with unknown amount of data By: pat on Thu, 30 September 1993 10:32
		Re: Reading files with unknown amount of data By: jim on Thu, 30 September 1993 10:47
		Re: Reading files with unknown amount of dat By: oet on Fri, 05 November 1993 00:28

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