From bug-request at octave dot org Wed Apr  5 14:28:43 2006
Subject: Plot should be able to handle empty vector inputs
From: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>
To: Quentin Spencer <qspencer at ieee dot org>
Cc: octave bug mailing list <bug at octave dot org>
Date: Wed, 5 Apr 2006 15:28:27 -0400

On  5-Apr-2006, Quentin Spencer wrote:

| In Matlab, it is possible to call the plot function with empty data.
| This is an error
|  >> plot([])
| ??? Error using ==> plot
| Vectors must be the same lengths.
| 
| However, this is acceptable.
|  >> plot([],[])
| 
| 
| In octave, I get the following error:
| oct 1> plot([],[])
| error: __plt2__: invalid data for plotting
| error: evaluating if command near line 48, column 3
| error: called from `__plt2__' in file 
| `/usr/share/octave/2.9.4/m/plot/__plt2__.m'
| error: evaluating if command near line 58, column 4
| error: evaluating if command near line 56, column 2
| error: evaluating if command near line 55, column 7
| error: evaluating while command near line 44, column 5
| error: evaluating if command near line 34, column 3
| error: called from `__plt__' in file 
| `/usr/share/octave/2.9.4/m/plot/__plt__.m'
| error: called from `plot' in file `/usr/share/octave/2.9.4/m/plot/plot.m'
| 
| Supporting this behavior is useful because I have a situation where I'm 
| plotting several vectors, and one pair of them may be empty, but I don't 
| know in advance without extra code to check for it. As you can see, this 
| is version 2.9.4, but looking at CVS, it looks like this hasn't changed 
| since then.

kHow about the following change.  I think it does what you want, but
I've not done a lot of testing.

| I might be able to write a patch for this, but I don't have 
| time right now--maybe later if I'm the first one to get to it.

Oops, sorry.  Well, instead of a patch, can you at do some testing of
the one below?

Thanks,

jwe


scripts/ChangeLog:

2006-04-05  John W. Eaton  <jwe at octave dot org>

	* plot/__plt2__.m: Return data = [] and fmtstr = "" if x1 and x2
	are both empty.
	* plot/__plt__.m: Ignore empty data and format strings returned
	from __plt1__ or __plt2__.


Index: scripts/plot/__plt2__.m
===================================================================
RCS file: /cvs/octave/scripts/plot/__plt2__.m,v
retrieving revision 1.15
diff -u -r1.15 __plt2__.m
--- scripts/plot/__plt2__.m	8 Sep 2005 01:40:58 -0000	1.15
+++ scripts/plot/__plt2__.m	5 Apr 2006 19:25:16 -0000
 at @ -67,6 +67,9 @@
     else
       error ("__plt2__: invalid data for plotting");
     endif
+  elseif (isempty (x1) && isempty (x2))
+    data = [];
+    fmtstr = "";
   else
     error ("__plt2__: invalid data for plotting");
   endif
Index: scripts/plot/__plt__.m
===================================================================
RCS file: /cvs/octave/scripts/plot/__plt__.m,v
retrieving revision 1.36
diff -u -r1.36 __plt__.m
--- scripts/plot/__plt__.m	13 Oct 2005 17:51:19 -0000	1.36
+++ scripts/plot/__plt__.m	5 Apr 2006 19:25:16 -0000
 at @ -56,11 +56,15 @@
 	if (x_set)
 	  fmt = __pltopt__ (caller, next_arg);
 	  if (y_set)
-	    [__plot_data__{__current_figure__}{__multiplot_xi__,__multiplot_yi__}{j}, fmtstr] = __plt2__ (x, y, fmt);
+	    [tdata, tfmtstr] = __plt2__ (x, y, fmt);
 	  else
-	    [__plot_data__{__current_figure__}{__multiplot_xi__,__multiplot_yi__}{j}, fmtstr] = __plt1__ (x, fmt);
+	    [tdata, tfmtstr] = __plt1__ (x, fmt);
+	  endif
+	  if (! isempty (tdata))
+	    __plot_data__{__current_figure__}{__multiplot_xi__,__multiplot_yi__}{j} = tdata;
+	    fmtstr = tfmtstr;
+	    have_data = true;
 	  endif
-	  have_data = true;
 	  x_set = false;
 	  y_set = false;
 	else
 at @ -69,8 +73,12 @@
       elseif (x_set)
 	if (y_set)
 	  fmt = __pltopt__ (caller, "");
-	  [__plot_data__{__current_figure__}{__multiplot_xi__,__multiplot_yi__}{j}, fmtstr] = __plt2__ (x, y, fmt);
-	  have_data = true;
+	  [tdata, tfmtstr] = __plt2__ (x, y, fmt);
+	  if (! isempty (tdata))
+	    __plot_data__{__current_figure__}{__multiplot_xi__,__multiplot_yi__}{j} = tdata;
+	    fmtstr = tfmtstr;
+	    have_data = true;
+	  endif
 	  x = next_arg;
 	  y_set = false;
 	else
 at @ -105,10 +113,10 @@
 
     __plot_data_offset__{__current_figure__}(__multiplot_xi__,__multiplot_yi__) = j;
 
-    if (! isempty (__plot_command__{__current_figure__}{__multiplot_xi__,__multiplot_yi__}))
-      if (__multiplot_mode__)
-	__gnuplot_raw__ ("clear\n");
-      endif
+    if (__multiplot_mode__)
+      __gnuplot_raw__ ("clear\n");
+    endif
+    if (! strcmp (__plot_command__{__current_figure__}{__multiplot_xi__,__multiplot_yi__}, "__gnuplot_plot__"))
       eval (__plot_command__{__current_figure__}{__multiplot_xi__,__multiplot_yi__});
     endif
 



-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
Subscription information:  http://www.octave.org/archive.html
-------------------------------------------------------------