Re: df_readline() question

[Philipp K. Janert]

> >
> > However, this is not how it seems to work. If there are
> > fields in the data file that cannot be transformed to double,
> > df_readline simply skips the line.
>
> That's certainly not true in general, or it wouldn't be able
> to handle files containing text fields.
> Also imageNaN.dem wouldn't provide the output it does.
>
> Simple test: feed it a file junk.dat:
>  1
>  2
>  junk
>  3
>  4
>
> gnuplot> plot 'junk.dat' with lp
>               ^
>          Bad data on line 3
> gnuplot>

Does plot do anything special here?

I have a situation (stolen from the fit function),
which basically says:

while( (i = readline(...)) != EOF ) {
        ...

And now I feed it your data file and it does NOT
return either DF_MISSING or DF_UNDEFINED!

So it strikes me as if it is not so much "more
complicated", but rather "more simple" cases
where it does the unexpected.

>
>
> But you could be right that there are more complicated cases where
> it unexpectedly fails to return a useful error indicator, or fails
> to return good values from a line that happens to contain a bad one.
>
> > I would have expected it
> > to return DF_MISSING or DF_UNDEFINED. But that's not
> > what I observe.
>
> From my personal TODO file:
>  - Sort out handling of junk/NaN/Inf in datafile.c
>    + using 1:2:3 and using ($1):($2):($3) should fill in all the legal
> values before returning an error code due to a single bad value

Based on your comment here, I just discovered that
if I enclose the columns in parens [that is using ($1):($2)]
rather than [using 1:2], then df_readline() DOES indeed
return DF_MISSING and DF_UNDEFINED.

Hm. I guess I knew this, although takes out of context like
this, it is surprising.

>    + new return code DF_INFINITY for Inf
>    + set datafile missing {"keyword"} {NaN} {Inf}
>      would explicitly treat NaN or Inf as a missing value, rather than a
> bad one + blank line should be distinguishable from a non-blank line
> containing junk + consistent treatement of NaN (always set point->type ==
> UNDEFINED)
>

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[Philipp K. Janert]

Comments at the end.

On Sunday 01 November 2009 10:38:04 pm Ethan Merritt (sfeam) wrote:

> On Sunday 01 November 2009, Philipp K. Janert wrote:
> > > Simple test: feed it a file junk.dat:
> > >  1
> > >  2
> > >  junk
> > >  3
> > >  4
> > >
> > > gnuplot> plot 'junk.dat' with lp
> > >               ^
> > >          Bad data on line 3
> > > gnuplot>
> >
> > Does plot do anything special here?
> >
> > I have a situation (stolen from the fit function),
> > which basically says:
> >
> > while( (i = readline(...)) != EOF ) {
> > ...
> >
> > And now I feed it your data file and it does NOT
> > return either DF_MISSING or DF_UNDEFINED!
>
> No, it returns 0.  But that's not EOF, so it should
> be catchable.

No, it doesn't. It does not return anything for the
line that contains "junk", when run with "using 1".

It does return -2 (DF_UNDEFINED) for the line
with "junk", but only when run with "using ($1)".


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[Ethan Merritt]

On Monday 02 November 2009 08:06:04 Philipp K. Janert wrote:

>
> Comments at the end.
>
> On Sunday 01 November 2009 10:38:04 pm Ethan Merritt (sfeam) wrote:
> > On Sunday 01 November 2009, Philipp K. Janert wrote:
> > > > Simple test: feed it a file junk.dat:
> > > >  1
> > > >  2
> > > >  junk
> > > >  3
> > > >  4
> > > >
> > > > gnuplot> plot 'junk.dat' with lp
> > > >               ^
> > > >          Bad data on line 3
> > > > gnuplot>
> > >
> > > Does plot do anything special here?
> > >
> > > I have a situation (stolen from the fit function),
> > > which basically says:
> > >
> > > while( (i = readline(...)) != EOF ) {
> > > ...
> > >
> > > And now I feed it your data file and it does NOT
> > > return either DF_MISSING or DF_UNDEFINED!
> >
> > No, it returns 0.  But that's not EOF, so it should
> > be catchable.
>
> No, it doesn't. It does not return anything for the
> line that contains "junk", when run with "using 1".
>
> It does return -2 (DF_UNDEFINED) for the line
> with "junk", but only when run with "using ($1)".

Hence the entry on my TODO list that I quoted earlier.
You could evaluate the following simple-minded patch:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
--- gnuplot/src/datafile.c 2009-10-10 11:43:30.000000000 -0700
+++ gnuplot-cvs/src/datafile.c 2009-11-02 08:53:58.000000000 -0800
@@ -1870,7 +1870,7 @@ df_readascii(double v[], int max)
  /* line bad only if user explicitly asked
  * for this column */
  if (df_no_use_specs)
-    line_okay = 0;
+    return DF_UNDEFINED;
  break;      /* return or ignore depending on line_okay */
     }
  }
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%5




--
Ethan A Merritt

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