Mercurial > octave-libgccjit
annotate scripts/statistics/base/median.m @ 8920:eb63fbe60fab
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| author | John W. Eaton <jwe@octave.org> |
|---|---|
| date | Sat, 07 Mar 2009 10:41:27 -0500 |
| parents | 81d6ab3ac93c |
| children | 1bf0ce0930be |
| rev | line source |
|---|---|
| 8920 | 1 ## Copyright (C) 1996, 1997, 1998, 1999, 2000, 2004, 2005, 2006, 2007, |
| 2 ## 2008, 2009 John W. Eaton | |
| 3200 | 3 ## |
| 4 ## This file is part of Octave. | |
| 5 ## | |
| 6 ## Octave is free software; you can redistribute it and/or modify it | |
| 7 ## under the terms of the GNU General Public License as published by | |
| 7016 | 8 ## the Free Software Foundation; either version 3 of the License, or (at |
| 9 ## your option) any later version. | |
| 3200 | 10 ## |
| 11 ## Octave is distributed in the hope that it will be useful, but | |
| 12 ## WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 13 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
| 14 ## General Public License for more details. | |
| 15 ## | |
| 16 ## You should have received a copy of the GNU General Public License | |
| 7016 | 17 ## along with Octave; see the file COPYING. If not, see |
| 18 ## <http://www.gnu.org/licenses/>. | |
| 3200 | 19 |
| 3367 | 20 ## -*- texinfo -*- |
| 6754 | 21 ## @deftypefn {Function File} {} median (@var{x}, @var{dim}) |
| 3367 | 22 ## If @var{x} is a vector, compute the median value of the elements of |
| 6754 | 23 ## @var{x}. If the elements of @var{x} are sorted, the median is defined |
| 24 ## as | |
| 3367 | 25 ## @iftex |
| 26 ## @tex | |
| 27 ## $$ | |
| 28 ## {\rm median} (x) = | |
| 29 ## \cases{x(\lceil N/2\rceil), & $N$ odd;\cr | |
| 30 ## (x(N/2)+x(N/2+1))/2, & $N$ even.} | |
| 31 ## $$ | |
| 32 ## @end tex | |
| 33 ## @end iftex | |
|
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34 ## @ifnottex |
| 3426 | 35 ## |
| 3367 | 36 ## @example |
| 37 ## @group | |
| 38 ## x(ceil(N/2)), N odd | |
| 3426 | 39 ## median(x) = |
| 3367 | 40 ## (x(N/2) + x((N/2)+1))/2, N even |
| 41 ## @end group | |
| 42 ## @end example | |
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43 ## @end ifnottex |
| 3367 | 44 ## If @var{x} is a matrix, compute the median value for each |
| 6754 | 45 ## column and return them in a row vector. If the optional @var{dim} |
| 46 ## argument is given, operate along this dimension. | |
| 5642 | 47 ## @seealso{std, mean} |
| 3367 | 48 ## @end deftypefn |
| 3200 | 49 |
| 50 ## Author: jwe | |
| 51 | |
| 4852 | 52 function retval = median (a, dim) |
| 3200 | 53 |
| 4852 | 54 if (nargin != 1 && nargin != 2) |
| 6046 | 55 print_usage (); |
| 4852 | 56 endif |
| 57 if (nargin < 2) | |
| 6024 | 58 dim = find (size (a) > 1, 1); |
| 4852 | 59 if (isempty (dim)) |
| 60 dim = 1; | |
| 61 endif | |
| 3200 | 62 endif |
| 63 | |
| 4852 | 64 sz = size (a); |
| 65 s = sort (a, dim); | |
| 5123 | 66 if (numel (a) > 0) |
| 4852 | 67 if (numel (a) == sz(dim)) |
| 68 if (rem (sz(dim), 2) == 0) | |
| 69 i = sz(dim) / 2; | |
| 70 retval = (s(i) + s(i+1)) / 2; | |
| 71 else | |
| 72 i = ceil (sz(dim) /2); | |
| 73 retval = s(i); | |
| 74 endif | |
| 3200 | 75 else |
| 4852 | 76 idx = cell (); |
| 77 nd = length (sz); | |
| 78 for i = 1:nd | |
| 79 idx{i} = 1:sz(i); | |
| 80 endfor | |
| 81 if (rem (sz(dim), 2) == 0) | |
| 82 i = sz(dim) / 2; | |
| 83 idx{dim} = i; | |
| 84 retval = s(idx{:}); | |
| 85 idx{dim} = i+1; | |
| 86 retval = (retval + s(idx{:})) / 2; | |
| 87 else | |
| 88 idx{dim} = ceil (sz(dim) / 2); | |
| 89 retval = s(idx{:}); | |
| 90 endif | |
| 3200 | 91 endif |
| 92 else | |
| 93 error ("median: invalid matrix argument"); | |
| 94 endif | |
| 95 | |
| 96 endfunction | |
| 7411 | 97 |
| 98 %!test | |
| 99 %! x = [1, 2, 3, 4, 5, 6]; | |
| 100 %! x2 = x'; | |
| 101 %! y = [1, 2, 3, 4, 5, 6, 7]; | |
| 102 %! y2 = y'; | |
| 103 %! | |
| 104 %! assert((median (x) == median (x2) && median (x) == 3.5 | |
| 105 %! && median (y) == median (y2) && median (y) == 4 | |
| 106 %! && median ([x2, 2*x2]) == [3.5, 7] | |
| 107 %! && median ([y2, 3*y2]) == [4, 12])); | |
| 108 | |
| 109 %!error median (); | |
| 110 | |
| 111 %!error median (1, 2, 3); | |
| 112 |