# HG changeset patch
# User pkienzle
# Date 1164946217 0
# Node ID 8d864908605d43ffe73357e0eb25f704a7aab8cf
# Parent  699db257153d05e0abdfbcd2467565e4c7b54d0d
Create a 2D histogram from x,y points

diff -r 699db257153d -r 8d864908605d main/plot/inst/hist2d.m
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/main/plot/inst/hist2d.m	Fri Dec 01 04:10:17 2006 +0000
@@ -0,0 +1,45 @@
+% hist2d ([x,y], xbins, ybins, norm)
+% Produce a 2D histogram.
+%
+% Points xi,yi are stored in a 2-column array.
+% If ybins is missing, use xbins.
+% If bins is a scalar, use that many bins.
+% If bins is a vector, it represents bin edges.
+
+% Author: Paul Kienzle
+% This code is public domain.
+
+function [ret_counts, xmid, ymid] = hist2d(M,xbins,ybins)
+
+  if nargin < 1 && nargin > 3, usage("[nn,xx] = hist2d (M,x,y)"); end
+
+  lo = min(M);
+  hi = max(M);
+  if nargin == 1
+    ybins = xbins = 10;
+  elseif nargin == 2
+    ybins = xbins;
+  endif
+
+  # If n bins, find centers based on n+1 bin edges
+  if isscalar(xbins) 
+    xbins = linspace(lo(1),hi(1),xbins+1); 
+    xbins = (xbins(1:end-1)+xbins(2:end))/2;
+  end
+  if isscalar(ybins)
+    ybins = linspace(lo(2),hi(2),ybins+1); 
+    ybins = (ybins(1:end-1)+ybins(2:end))/2;
+  end    
+
+  xcut = (xbins(1:end-1)+xbins(2:end))/2;
+  ycut = (ybins(1:end-1)+ybins(2:end))/2;
+  xidx = lookup(xcut,M(:,1))+1;
+  yidx = lookup(ycut,M(:,2))+1;
+  counts = sparse(xidx,yidx,1,length(xbins),length(ybins),'sum');
+
+  if nargout
+    ret_counts = full(counts);
+  else
+    mesh(xbins,ybins,full(counts));
+  end
+end