--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/scripts/sparse/spstats.m	Fri Feb 25 19:55:28 2005 +0000
@@ -0,0 +1,48 @@
+## Copyright (C) 2004 Paul Kienzle
+##
+## This program is free software and is in the public domain
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {[@var{count}, @var{mean}, @var{var}]} = spstats (@var{s})
+## @deftypefnx {Function File} {[@var{count}, @var{mean}, @var{var}]} = spstats (@var{s}, @var{j})
+## Return the stats for the non-zero elements of the sparse matrix @var{s}.
+## @var{count} is the number of non-zeros in each column, @var{mean}
+## is the mean of the non-zeros in each column, and @var{var} is the  
+## variance of the non-zeros in each column.
+##
+## Called with two output arguments, if @var{s} is the data and @var{j}
+## is the bin number for the data, compute the stats for each bin.  In 
+## this case, bins can contain data values of zero, whereas with 
+## @code{spstats (@var{s})} the zeros may disappear.
+## @end deftypefn
+
+function [count,mean,var] = spstats(S,j)
+  if nargin < 1 || nargin > 2
+    usage("[count, mean, var] = spstats(S)  OR  spstats(x,j)");
+  endif
+
+  [n, m] = size (S);
+  if nargin == 1
+    [i,j,v] = spfind (S);
+  else
+    v = S;    
+    i = 1:length (v);
+    S = sparse (i, j, v);
+  endif 
+
+  count = spsum (sparse (i, j, 1, n, m));
+  if (nargout > 1) 
+    mean = spsum(S) ./ count; 
+  end
+  if (nargout > 2) 
+    ## XXX FIXME XXX Variance with count = 0 or 1?
+    diff = S - sparse (i, j, mean(j), n, m); 
+    var = spsum (diff .* diff) ./ (count - 1);
+  end
+endfunction
+
+%!test
+%! [n,m,v] = spstats([1 2 1 2 3 4],[2 2 1 1 1 1]);
+%! assert(n,[4,2]);
+%! assert(m,[10/4,3/2],10*eps);
+%! assert(v,[5/3,1/2],10*eps);