--- a/scripts/ChangeLog
+++ b/scripts/ChangeLog
@@ -1,3 +1,10 @@
+2010-03-19  Rik  <octave@nomad.inbox5.com>
+
+	* general/module.mk, statistics/base/module.mk: Move runlength.m
+	to statistics/base directory.
+	* statistics/base/runlength.m: Add input validation and tests.
+	Improve docstring.
+
 2010-03-19  Rik  <octave@nomad.inbox5.com>
 
 	* statistics/models/logistic_regression.m: Do not split function

--- a/scripts/general/module.mk
+++ b/scripts/general/module.mk
@@ -70,7 +70,6 @@
   general/repmat.m \
   general/rot90.m \
   general/rotdim.m \
-  general/runlength.m \
   general/saveobj.m \
   general/shift.m \
   general/shiftdim.m \

--- a/scripts/statistics/base/module.mk
+++ b/scripts/statistics/base/module.mk
@@ -28,6 +28,7 @@
   statistics/base/range.m \
   statistics/base/ranks.m \
   statistics/base/run_count.m \
+  statistics/base/runlength.m \
   statistics/base/skewness.m \
   statistics/base/spearman.m \
   statistics/base/statistics.m \

rename from scripts/general/runlength.m
rename to scripts/statistics/base/runlength.m
--- a/scripts/general/runlength.m
+++ b/scripts/statistics/base/runlength.m
@@ -17,7 +17,7 @@
 ## <http://www.gnu.org/licenses/>.
 
 ## -*- texinfo -*-
-## @deftypefn {Function File} {} runlength (@var{x})
+## @deftypefn {Function File} {[count, value] =} runlength (@var{x})
 ## Find the lengths of all sequences of common values.  Return the
 ## vector of lengths and the value that was repeated.
 ##
@@ -30,9 +30,34 @@
 ## @end deftypefn
 
 function [count, value] = runlength (x)
+  if (nargin != 1)
+    print_usage ();
+  endif
+
+  if (!isnumeric (x) || !isvector (x))
+    error ("runlength: X must be a numeric vector");
+  endif
+
+  if (iscolumn (x))
+    x = x.';
+  endif
+
   idx = [find(x(1:end-1) != x(2:end)), length(x)];
-  value = x(idx);
   count = diff ([0 idx]);
+  if (nargout == 2)
+    value = x(idx);
+  endif
 endfunction
 
 %!assert (runlength([2 2 0 4 4 4 0 1 1 1 1]), [2 1 3 1 4]);
+%!assert (runlength([2 2 0 4 4 4 0 1 1 1 1]'), [2 1 3 1 4]);
+%!test
+%! [c, v] = runlength ([2 2 0 4 4 4 0 1 1 1 1]);
+%! assert (c, [2 1 3 1 4]);
+%! assert (v, [2 0 4 0 1]);
+
+%% Test input validation
+%!error runlength ()
+%!error runlength (1, 2)
+%!error runlength (true(1,2))
+%!error runlength (ones(2,2))