bugGNU Octave - Bugs: bug #37023, strread with leading white space...

 
 

bug #37023: strread with leading white space in new lines

Submitted by:  Xuejin Wang <fclxc10>
Submitted on:  Fri 03 Aug 2012 10:58:48 PM UTC  
 
Category:  None Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Incorrect Result
Status:  Fixed Assigned to:  Philip Nienhuis <philipnienhuis>
Originator Name:  Xuejin Wang Open/Closed:  Closed
Release:  3.6.1 Operating System:  Any

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Thu 30 Aug 2012 07:00:16 PM UTC, comment #4:

Finally fixed in this changeset:
http://hg.savannah.gnu.org/hgweb/octave/rev/2136343014d5

Philip Nienhuis <philipnienhuis>
Project MemberIn charge of this item.
Thu 16 Aug 2012 09:48:58 AM UTC, comment #3:

Sorry, that should read:

Change lines 378-379 in strread.m from:

into these three lines:

(watch out for line wrap)

Philip Nienhuis <philipnienhuis>
Project MemberIn charge of this item.
Thu 16 Aug 2012 09:45:52 AM UTC, comment #2:

Your analysis is spot on, Xuejin.
While strread.m by itself parses similar strings OK, this bug was hidden because of the way strread.m is invoked by textscan.m and textscan.m only has tests specific to specific textscan options.

... but:

Cause: I didn't realize in full that regexprep() doesn't "do" overlapping matches. I don't know if that is documented.

Once I'm back at my dev machine I'll push a fix + extra tests (hopefully end of next week).
You'll probably have to wait for Octave-3.8 or 4.0, so that's why I suggest the fix below if you're in a hurry:

FIX (for Octave-3.6.2):
Change lines 378 in strread.m from:
into these three lines:
(watch out for line wrap!)

Philip Nienhuis <philipnienhuis>
Project MemberIn charge of this item.
Tue 14 Aug 2012 09:53:07 AM UTC, comment #1:

(Sorry for late reply, I'm on vacation abroad w/o much Internet access)

The example file you posted contains an empty line. Is that correct?
When I interpret your datafile as

" 1. 1 \n 2 3\n"

I get:

...which indeed looks suspicious. I'll have a look at it in the next weeks.

As a workaround, you can also specify the "whitespace" parameter:

Thanks for the report.

Philip Nienhuis <philipnienhuis>
Project MemberIn charge of this item.
Fri 03 Aug 2012 10:58:48 PM UTC, original submission:

When using textscan to read some data from a text file, if a new line starts with a space and the previous line ends with a space, the first data in that line becomes "NaN".

For example, if the text file is as follows:

  1. 1

2 3
It has two lines, each line starts with a space. The following command is used for reading the file:

data = textscan(fid,'%f %f')

The first line is always OK. If the first line has no space at its end, the second line is also OK. However if the first line has a space at the end (after the number "1" at the end of line 1), the first column becomes [0 NaN 3]', and the second column is [1 2]'.

I traced the problem to the function strread, line 373-380:

## Check for single delimiter followed/preceded by whitespace
## FIXME: Double strrep on str is enormously expensive of CPU time.
## Can this be eliminated
if (! isempty (delimiter_str))
dlmstr = setdiff (delimiter_str, " ");
rxp_dlmwsp = sprintf ("( [%s]|[%s] )", dlmstr, dlmstr);
str = regexprep (str, rxp_dlmwsp, delimiter_str(1));
endif

My workaround is to run line 381-387 before the above lines. Maybe you'll have a better solution for it.

Thanks,
Xuejin

Xuejin Wang <fclxc10>

 

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    Follow 7 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2012-08-30 philipnienhuis StatusIn Progress => Fixed
        Originator Name => Xuejin Wang
        Open/ClosedOpen => Closed
    2012-08-16 philipnienhuis StatusConfirmed => In Progress
    2012-08-14 philipnienhuis StatusNone => Confirmed
        Assigned toNone => philipnienhuis
        Operating SystemMicrosoft Windows => Any

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