annotate scripts/statistics/base/median.m @ 14570:d07d96e53612 stable

seconds after the minute can be 0-60, not 0-61 * system.txi (Timing Utilities): Correct possible values for number of seconds in time structures. From Rafael Arndt <rafaelarndt@gmail.com>.
author John W. Eaton <jwe@octave.org>
date Tue, 17 Apr 2012 14:42:49 -0400
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children 12ccdce2c216
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1 ## Copyright (C) 1996-2012 John W. Eaton
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2 ## Copyright (C) 2009-2010 VZLU Prague
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3 ##
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4 ## This file is part of Octave.
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5 ##
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6 ## Octave is free software; you can redistribute it and/or modify it
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7 ## under the terms of the GNU General Public License as published by
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8 ## the Free Software Foundation; either version 3 of the License, or (at
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9 ## your option) any later version.
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10 ##
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11 ## Octave is distributed in the hope that it will be useful, but
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12 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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13 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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14 ## General Public License for more details.
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15 ##
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16 ## You should have received a copy of the GNU General Public License
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17 ## along with Octave; see the file COPYING. If not, see
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18 ## <http://www.gnu.org/licenses/>.
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19
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20 ## -*- texinfo -*-
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21 ## @deftypefn {Function File} {} median (@var{x})
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22 ## @deftypefnx {Function File} {} median (@var{x}, @var{dim})
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23 ## Compute the median value of the elements of the vector @var{x}.
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24 ## If the elements of @var{x} are sorted, the median is defined
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25 ## as
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26 ## @tex
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27 ## $$
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28 ## {\rm median} (x) =
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29 ## \cases{x(\lceil N/2\rceil), & $N$ odd;\cr
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30 ## (x(N/2)+x(N/2+1))/2, & $N$ even.}
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31 ## $$
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32 ## @end tex
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33 ## @ifnottex
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34 ##
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35 ## @example
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36 ## @group
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37 ## x(ceil(N/2)) N odd
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38 ## median (x) =
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39 ## (x(N/2) + x((N/2)+1))/2 N even
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40 ## @end group
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41 ## @end example
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42 ##
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43 ## @end ifnottex
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44 ## If @var{x} is a matrix, compute the median value for each
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45 ## column and return them in a row vector. If the optional @var{dim}
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46 ## argument is given, operate along this dimension.
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47 ## @seealso{mean, mode}
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48 ## @end deftypefn
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49
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50 ## Author: jwe
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51
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52 function retval = median (x, dim)
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53
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54 if (nargin != 1 && nargin != 2)
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55 print_usage ();
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56 endif
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57
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58 if (! (isnumeric (x) || islogical (x)))
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59 error ("median: X must be a numeric vector or matrix");
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60 endif
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61
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62 if (isempty (x))
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63 error ("median: X cannot be an empty matrix");
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64 endif
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65
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66 nd = ndims (x);
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67 sz = size (x);
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68 if (nargin < 2)
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69 ## Find the first non-singleton dimension.
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70 (dim = find (sz > 1, 1)) || (dim = 1);
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71 else
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72 if (!(isscalar (dim) && dim == fix (dim))
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73 || !(1 <= dim && dim <= nd))
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74 error ("median: DIM must be an integer and a valid dimension");
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75 endif
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76 endif
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77
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78 n = sz(dim);
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79 k = floor ((n+1) / 2);
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80 if (mod (n, 2) == 1)
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81 retval = nth_element (x, k, dim);
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82 else
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83 retval = mean (nth_element (x, k:k+1, dim), dim);
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84 endif
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85 ## Inject NaNs where needed, to be consistent with Matlab.
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86 retval(any (isnan (x), dim)) = NaN;
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87
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88 endfunction
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89
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90
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91 %!test
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92 %! x = [1, 2, 3, 4, 5, 6];
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93 %! x2 = x';
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94 %! y = [1, 2, 3, 4, 5, 6, 7];
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95 %! y2 = y';
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96 %!
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97 %! assert(median (x) == median (x2) && median (x) == 3.5);
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98 %! assert(median (y) == median (y2) && median (y) == 4);
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99 %! assert(median ([x2, 2*x2]) == [3.5, 7]);
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100 %! assert(median ([y2, 3*y2]) == [4, 12]);
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101
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102 %% Test multidimensional arrays (bug #35679)
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103 %!shared a, b, x, y
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104 %! rand ("seed", 2);
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105 %! a = rand (2,3,4,5);
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106 %! b = rand (3,4,6,5);
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107 %! x = sort (a, 4);
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108 %! y = sort (b, 3);
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109 %!assert (median (a, 4), x(:, :, :, 3));
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110 %!assert (median (b, 3), (y(:, :, 3, :) + y(:, :, 4, :))/2);
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111
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112 %!assert(median (single([1,2,3])), single(2));
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113 %!assert(median ([1,2,NaN;4,5,6;NaN,8,9]), [NaN, 5, NaN]);
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114
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115 %% Test input validation
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116 %!error median ();
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117 %!error median (1, 2, 3);
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118 %!error median ({1:5});
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119 %!error median (['A'; 'B']);
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120 %!error median (1, ones(2,2));
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121 %!error median (1, 1.5);
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122 %!error median (1, 0);
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123