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## Copyright (C) 1995-2013 Kurt Hornik
##
## 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} {} iqr (@var{x})
## @deftypefnx {Function File} {} iqr (@var{x}, @var{dim})
## Return the interquartile range, i.e., the difference between the upper
## and lower quartile of the input data. If @var{x} is a matrix, do the
## above for first non-singleton dimension of @var{x}.
##
## If the optional argument @var{dim} is given, operate along this dimension.
##
## As a measure of dispersion, the interquartile range is less affected by
## outliers than either @code{range} or @code{std}.
## @seealso{range, std}
## @end deftypefn
## Author KH <Kurt.Hornik@wu-wien.ac.at>
## Description: Interquartile range
function y = iqr (x, dim)
if (nargin != 1 && nargin != 2)
print_usage ();
endif
if (! (isnumeric (x) || islogical (x)))
error ("iqr: X must be a numeric vector or matrix");
endif
nd = ndims (x);
sz = size (x);
nel = numel (x);
if (nargin != 2)
## Find the first non-singleton dimension.
(dim = find (sz > 1, 1)) || (dim = 1);
else
if (!(isscalar (dim) && dim == fix (dim))
|| !(1 <= dim && dim <= nd))
error ("iqr: DIM must be an integer and a valid dimension");
endif
endif
## This code is a bit heavy, but is needed until empirical_inv
## can take a matrix, rather than just a vector argument.
n = sz(dim);
sz(dim) = 1;
if (isa (x, "single"))
y = zeros (sz, "single");
else
y = zeros (sz);
endif
stride = prod (sz(1:dim-1));
for i = 1 : nel / n;
offset = i;
offset2 = 0;
while (offset > stride)
offset -= stride;
offset2++;
endwhile
offset += offset2 * stride * n;
rng = [0 : n-1] * stride + offset;
y(i) = diff (empirical_inv ([1/4, 3/4], x(rng)));
endfor
endfunction
%!assert (iqr (1:101), 50)
%!assert (iqr (single (1:101)), single (50))
%%!test
%%! x = [1:100];
%%! n = iqr (x, 0:10);
%%! assert (n, [repmat(100, 1, 10), 1]);
%!error iqr ()
%!error iqr (1, 2, 3)
%!error iqr (1)
%!error iqr (['A'; 'B'])
%!error iqr (1:10, 3)
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