Re: newline in strread format

[Ben Abbott]

On Jun 24, 2014, at 4:15 AM, Daniel J Sebald <address@hidden> wrote:

> On 06/23/2014 10:57 PM, John W. Eaton wrote:
>> I think the following should work, but it's throwing an error:
>> 
>> octave:1> [a, b, c] = strread ("1 2 3\n4 5 6\n7 8 9\n", "%f %f %f\n")
>> strread: FORMAT does not match data
>> error: called from 'strread' in file
>> /home/jwe/src/octave-stable/scripts/io/strread.m near line 745, column 13
>> error: called from:
>> error: /home/jwe/src/octave-stable/scripts/io/strread.m at line 755,
>> column 9
>> 
>> I took a look at strread.m but I'm not sure what the right approach is
>> for a fix. It appears to me that newlines are removed from the string
>> and that it is split on the field delimiter. But the newline
>> character remains in the list of format specifiers.
>> 
>> I noticed the problem in the stable sources, but it seems to also be
>> present in the current sources on the default branch.
>> 
>> Any clues would be much appreciated.
> 
> I suppose that "\n" could in theory be a valid literal.  That's where the 
> interpretation part of this routine is failing, i.e., "\n" as not being 
> accepted as a literal.  Consider that the following works:
> 
> octave:3> [a, b, c] = strread ("1 2 3L\n4 5 6L\n7 8 9L\n", "%f %f %fL")
> a =
> 
>   1
>   4
>   7
> 
> b =
> 
>   2
>   5
>   8
> 
> c =
> 
>   3
>   6
>   9
> 
> The newline character is always the character that can be treated as a "new 
> line" in the data string.  That is, if we replace literal "L" with "\n":
> 
> [a, b, c] = strread ("1 2 3\n\n4 5 6\n\n7 8 9\n\n", "%f %f %f\n")
> 
> one would think that we should get the same result.  (Notice the two newline 
> characters in the data string.)  But that fails as well.
> 
> octave:4> [a, b, c] = strread ("1 2 3\n\n4 5 6\n\n7 8 9\n\n", "%f %f %f\n")
> strread: FORMAT does not match data
> error: called from 'strread' in file 
> /usr/local/src/octave/octave-for_loop_test/build-dev/../octave-dev/scripts/io/strread.m
>  near line 745, column 13
> error: called from:
> error: 
> /usr/local/src/octave/octave-for_loop_test/build-dev/../octave-dev/scripts/io/strread.m
>  at line 755, column 9
> 
> One could maybe make sense of the single literal newline characters in the 
> following way:
> 
> octave:4> [a, b, c, d, e, f, g, h, i] = strread ("1 2 3\n4 5 6\n7 8 9\n", "%f 
> %f %f\n%f %f %f\n%f %f %f\n")
> warning: strread: unable to parse text or file with given format string
> warning: called from
>    strread at line 659 column 7
> error: element number 1 undefined in return list
> 
> but as seen above, that fails too.
> 
> Dan

For reference, this works in Matlab.

[a, b, c] = strread (sprintf ('1 2 3\n4 5 6\n7 8 9\n'), '%f %f %f\n')

a =

     1
     4
     7


b =

     2
     5
     8


c =

     3
     6
     9

Same result for

[a, b, c] = strread (sprintf ('1 2 3\n4 5 6\n7 8 9\n'), '%f %f %f')

and

[a, b, c] = strread (sprintf ('1 2 3 4 5 6 7 8 9'), '%f %f %f')

This particular feature (of implicit \n in the format) is confusing for me.

Ben