comp.lang.idl-pvwave archive: archive » Re: Reading columns of binary data

Home » Public Forums » archive » Re: Reading columns of binary data

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: Reading columns of binary data [message #49602 is a reply to message #49601]

Mon, 07 August 2006 10:41

news.verizon.net
Messages: 47
Registered: August 2003

Member

>
> ; openr, 1, ...
> arr=assoc(1, data)
> result=arr[0:*:100]
>
> however, it has a big disadvantage of using huge memory for data. My
> feature request would be an "assoc, unit, type, dimensions, [offset]"
> system function, as the value of data in never used.
>

Yes, I agree with that feature request. But even if it were
implemented I'm not sure that it solves my original question. From
the documentation for ASSOC about multiple subscripts

"Although the ability to directly refer to array elements within an
associated file can be convenient, it can also be very slow because
every access to an array element causes the entire array to be
transferred to or from memory."

So my impression is that this is not any better than reading the entire
array and subscripting a column.

--Wayne

P.S. Anybody know if the V6.3 documentation below from ASSOC() is still
valid? I stopped worrying about the block size of file system
years ago.

"Arrays are accessed most efficiently if their length is an integer
multiple of the block size of the filesystem holding the file. Common
values are powers of 2, such as 512, 2K (2048), 4K (4096), or 8K (8192)
bytes. For example, on a disk with 512-byte blocks, one benchmark
program required approximately one-eighth of the time required to read
a 512 x 512-byte image that started and ended on a block boundary, as
compared to a similar program that read an image that was not stored on
even block boundaries. "

Report message to a moderator

[Message index]

		Re: Reading columns of binary data By: Wayne Landsman on Mon, 07 August 2006 15:21
		Re: Reading columns of binary data By: JD Smith on Mon, 07 August 2006 14:54
		Re: Reading columns of binary data By: Foldy Lajos on Mon, 07 August 2006 11:07
		Re: Reading columns of binary data By: news.verizon.net on Mon, 07 August 2006 10:41
		Re: Reading columns of binary data By: Foldy Lajos on Mon, 07 August 2006 10:30
		Re: Reading columns of binary data By: Foldy Lajos on Tue, 08 August 2006 07:57
		Re: Reading columns of binary data By: JD Smith on Mon, 07 August 2006 15:44

Previous Topic:	Problems with plotting in histogram mode
Next Topic:	Re: Problems with plotting in histogram mode

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Fri Oct 10 04:11:49 PDT 2025

Total time taken to generate the page: 0.15655 seconds