Re: fast scatter plots - advice sought

[David Bateman]

Jaroslav Hajek wrote:
> On Fri, Jan 15, 2010 at 3:06 PM, dbateman <address@hidden> wrote:
>   
> > Ok, so given this and the feedback from Shai both scatter and the gnuplot
> > backend do the wrong thing here. I'll fix this over the weekend.
> >
> > Thanks
> > David
> >
> >     
>
> I didn't quite follow the information flow, but I noted that if in
> Matlab you do scatter (x, y, s, c) where x, y, c are long column
> vectors and s is a scalar, Matlab creates a single patch that can
> handle the varying color, through property VertexCData or something
> like that. Is this possible for Octave? If so, then in this case one
> would not need to split by unique colors and sizes, but just by sizes,
> which would probably be much faster when variable colors are used.
>
> OTOH, when colors are specified as a full RGB Nx3 array, Matlab (2007)
> seems to invariably make one patch per point.
>
>   
Jaroslav,

It appears that gnuplot can handle a PM3D palette for lines in 2 and 3D, 
so can be quite easily handled in gnuplot itself. Something like the 
attached patch seems to work and the example

n=5000;x = randn(1,n); y = randn(1,n); c = sqrt(x.^2+y.^2); h = 
scatter(x,y,6,c)

is now quite fast with gnuplot. Do you see any issues with making a 
change like this?

D.

diff --git a/scripts/plot/__go_draw_axes__.m b/scripts/plot/__go_draw_axes__.m
--- a/scripts/plot/__go_draw_axes__.m
+++ b/scripts/plot/__go_draw_axes__.m
@@ -762,10 +762,10 @@
                   if (numel(ccol) == 3)
                     color = ccol;
                   else
-                    r = 1 + round ((size (cmap, 1) - 1)
-                                   * (ccol - clim(1))/(clim(2) - clim(1)));
-                    r = max (1, min (r, size (cmap, 1)));
-                    color = cmap(r, :);
+                     if (isscalar (ccol))
+                       ccol = repmat(ccol, numel (xcol), 1);
+                     endif
+                     color = "flat";
                   endif
                 elseif (strncmp (ec, "interp", 6))
                   warning ("\"interp\" not supported, using 1st entry of 
cdata");
@@ -859,8 +859,12 @@
             if (mono)
               colorspec = "";
             else
-              colorspec = sprintf ("lc rgb \"#%02x%02x%02x\"",
-                                   round (255*color));
+               if (ischar (color))
+                 colorspec = "palette";
+               else
+                colorspec = sprintf ("lc rgb \"#%02x%02x%02x\"",
+                                     round (255*color));
+               endif
             endif
 
              sidx = 1;
@@ -993,20 +997,40 @@
               withclause{data_idx} = tmpwith{1};
              endif
             if (nd == 3)
-              if (! isnan (xcol) && ! isnan (ycol) && ! isnan (zcol))
-                data{data_idx} = [[xcol; xcol(1)], [ycol; ycol(1)], ...
-                                  [zcol; zcol(1)]]';
-              else
-                data{data_idx} = [xcol, ycol, zcol]';
-              endif
-              usingclause{data_idx} = sprintf ("record=%d using 
($1):($2):($3)", columns (data{data_idx}));
+               if (ischar (color))
+                if (! isnan (xcol) && ! isnan (ycol) && ! isnan (zcol))
+                  data{data_idx} = [[xcol; xcol(1)], [ycol; ycol(1)], ...
+                                    [zcol; zcol(1)]]';
+                else
+                  data{data_idx} = [xcol, ycol, zcol]';
+                endif
+                usingclause{data_idx} = sprintf ("record=%d using 
($1):($2):($3)", columns (data{data_idx}));
+               else
+                if (! isnan (xcol) && ! isnan (ycol) && ! isnan (zcol))
+                  data{data_idx} = [[xcol; xcol(1)], [ycol; ycol(1)], ...
+                                    [zcol; zcol(1)], [ccol; ccol(1)]]';
+                else
+                  data{data_idx} = [xcol, ycol, zcol, ccol]';
+                endif
+                usingclause{data_idx} = sprintf ("record=%d using 
($1):($2):($3):($4)", columns (data{data_idx}));
+               endif
             else
-              if (! isnan (xcol) && ! isnan (ycol))
-                data{data_idx} = [[xcol; xcol(1)], [ycol; ycol(1)]]';
-              else
-                data{data_idx} = [xcol, ycol]';
-              endif
-              usingclause{data_idx} = sprintf ("record=%d using ($1):($2)", 
columns (data{data_idx}));
+               if (ischar (color))
+                if (! isnan (xcol) && ! isnan (ycol))
+                  data{data_idx} = [[xcol; xcol(1)], [ycol; ycol(1)], ...
+                                     [ccol; ccol(1)]]';
+                else
+                  data{data_idx} = [xcol, ycol, ccol]';
+                endif
+                usingclause{data_idx} = sprintf ("record=%d using 
($1):($2):($3)", columns (data{data_idx}));
+               else
+                if (! isnan (xcol) && ! isnan (ycol))
+                  data{data_idx} = [[xcol; xcol(1)], [ycol; ycol(1)]]';
+                else
+                  data{data_idx} = [xcol, ycol]';
+                endif
+                usingclause{data_idx} = sprintf ("record=%d using ($1):($2)", 
columns (data{data_idx}));
+               endif
             endif
 
             if (length (tmpwith) > 1)
diff --git a/scripts/plot/private/__scatter__.m 
b/scripts/plot/private/__scatter__.m
--- a/scripts/plot/private/__scatter__.m
+++ b/scripts/plot/private/__scatter__.m
@@ -186,18 +186,7 @@
     if (ischar (c) || rows (c) == 1)
       h = render_size_color (hg, vert, s, c, marker, filled, false); 
     else
-      [cc, idx] = unique_idx (c, "rows");
-      if (isscalar (s))
-        for i = 1:rows (x)
-          h = render_size_color (hg, vert(idx{i},:), s, cc(i,:), 
-                                 marker, filled, true);
-        endfor
-      else
-        for i = 1:rows (x)
-          h = render_size_color (hg, vert(idx{i},:), s(idx{i}), cc(i,:), 
-                                 marker, filled, true);
-        endfor
-      endif
+      h = render_size_color (hg, vert, s, c, marker, filled, true); 
     endif
 
   endif