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[CreaPhase.git] / octave_packages / m / general / shiftdim.m

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+## Copyright (C) 2004-2012 John Eaton and David Bateman
+##
+## This file is part of Octave.
+##
+## Octave is free software; you can redistribute it and/or modify it
+## under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 3 of the License, or (at
+## your option) any later version.
+##
+## Octave is distributed in the hope that it will be useful, but
+## WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+## General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with Octave; see the file COPYING.  If not, see
+## <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn  {Function File} {@var{y} =} shiftdim (@var{x}, @var{n})
+## @deftypefnx {Function File} {[@var{y}, @var{ns}] =} shiftdim (@var{x})
+## Shift the dimensions of @var{x} by @var{n}, where @var{n} must be
+## an integer scalar.  When @var{n} is positive, the dimensions of
+## @var{x} are shifted to the left, with the leading dimensions
+## circulated to the end.  If @var{n} is negative, then the dimensions
+## of @var{x} are shifted to the right, with @var{n} leading singleton
+## dimensions added.
+##
+## Called with a single argument, @code{shiftdim}, removes the leading
+## singleton dimensions, returning the number of dimensions removed
+## in the second output argument @var{ns}.
+##
+## For example:
+##
+## @example
+## @group
+## x = ones (1, 2, 3);
+## size (shiftdim (x, -1))
+##    @result{} [1, 1, 2, 3]
+## size (shiftdim (x, 1))
+##    @result{} [2, 3]
+## [b, ns] = shiftdim (x)
+##    @result{} b = [1, 1, 1; 1, 1, 1]
+##    @result{} ns = 1
+## @end group
+## @end example
+## @seealso {reshape, permute, ipermute, circshift, squeeze}
+## @end deftypefn
+
+function [y, ns]  = shiftdim (x, n)
+
+  if (nargin < 1 || nargin > 2)
+    print_usage ();
+  endif
+
+  nd = ndims (x);
+  orig_dims = size (x);
+
+  if (nargin == 1)
+    ## Find the first non-singleton dimension.
+    (n = find (orig_dims != 1, 1) - 1) || (n = nd);
+  elseif (! (isscalar (n) && n == fix (n)))
+    error ("shiftdim: N must be a scalar integer");
+  endif
+
+  if (n >= nd)
+    n = rem (n, nd);
+  endif
+
+  if (n < 0)
+    singleton_dims = ones (1, -n);
+    y = reshape (x, [singleton_dims, orig_dims]);
+  elseif (n > 0)
+    ## We need permute here instead of reshape to shift values in a
+    ## compatible way.
+    y = permute (x, [n+1:nd 1:n]);
+  else
+    y = x;
+  endif
+
+  ns = n;
+
+endfunction
+
+
+%!test
+%! x = rand (1, 1, 4, 2);
+%! [y, ns] = shiftdim (x);
+%! assert (size (y), [4 2]);
+%! assert (ns, 2);
+%! assert (shiftdim (y, -2), x);
+%! assert (size (shiftdim (x, 2)), [4 2]);
+%!assert (size (shiftdim (rand (0, 1, 2))), [0 1 2]);
+
+%% Test input validation
+%!error(shiftdim ());
+%!error(shiftdim (1,2,3));
+%!error(shiftdim (1, ones (2)));
+%!error(shiftdim (1, 1.5));
+