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new function: accumdim
author Jaroslav Hajek <highegg@gmail.com>
date Fri, 05 Mar 2010 11:11:01 +0100
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10394:bc475cd49147 10395:aeb5b1e47978
1 ## Copyright (C) 2010 VZLU Prague
2 ##
3 ## This file is part of Octave.
4 ##
5 ## Octave is free software; you can redistribute it and/or modify it
6 ## under the terms of the GNU General Public License as published by
7 ## the Free Software Foundation; either version 3 of the License, or (at
8 ## your option) any later version.
9 ##
10 ## Octave is distributed in the hope that it will be useful, but
11 ## WITHOUT ANY WARRANTY; without even the implied warranty of
12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 ## General Public License for more details.
14 ##
15 ## You should have received a copy of the GNU General Public License
16 ## along with Octave; see the file COPYING. If not, see
17 ## <http://www.gnu.org/licenses/>.
18
19 ## -*- texinfo -*-
20 ## @deftypefn {Function File} {} accumdim (@var{subs}, @var{vals}, @var{dim}, @var{sz}, @var{func}, @var{fillval})
21 ## Create an array by accumulating the slices of an array into the
22 ## positions defined by their subscripts along a specified dimension.
23 ## The subscripts are defined by the index vector @var{subs}.
24 ## The dimension is specified by @var{dim}. If not given, it defaults
25 ## to the first non-singleton dimension.
26 ##
27 ## The extent of the result matrix in the working dimension will be determined
28 ## by the subscripts themselves.
29 ## However, if @var{n} is defined it determines this extent.
30 ##
31 ## The default action of @code{accumdim} is to sum the subarrays with the
32 ## same subscripts. This behavior can be modified by defining the @var{func}
33 ## function. This should be a function or function handle that accepts an
34 ## array and a dimension, and reduces the array along this dimension.
35 ## As a special exception, the built-in @code{min} and @code{max} functions
36 ## can be used directly, and @code{accumdim} accounts for the middle empty
37 ## argument that is used in their calling.
38 ##
39 ## The slices of the returned array that have no subscripts associated with
40 ## them are set to zero. Defining @var{fillval} to some other value allows
41 ## these values to be defined.
42 ##
43 ## An example of the use of @code{accumarray} is:
44 ##
45 ## @example
46 ## @group
47 ## accumarray ([1,1,1;2,1,2;2,3,2;2,1,2;2,3,2], 101:105)
48 ## @result{} ans(:,:,1) = [101, 0, 0; 0, 0, 0]
49 ## ans(:,:,2) = [0, 0, 0; 206, 0, 208]
50 ## @end group
51 ## @end example
52 ##
53 ## @seealso{accumarray}
54 ## @end deftypefn
55
56 function A = accumdim (subs, val, dim, n = 0, func = [], fillval = 0)
57
58 if (nargin < 2 || nargin > 5)
59 print_usage ();
60 endif
61
62 if (isempty (fillval))
63 fillval = 0;
64 endif
65
66 if (isempty (func))
67 func = @sum;
68 endif
69
70 if (! isvector (subs))
71 error ("accumdim: subs must be a subscript vector");
72 elseif (! isindex (subs)) # creates index cache
73 error ("accumdim: indices must be positive integers");
74 else
75 m = max (subs);
76 if (n == 0)
77 n = m;
78 elseif (n < m)
79 error ("accumdim: index out of range")
80 endif
81 endif
82
83 ## The general case.
84 sz = size (val);
85
86 if (nargin < 3)
87 [~, dim] = max (sz != 1); # first non-singleton dim
88 elseif (! isindex (dim, ndims (val)))
89 error ("accumdim: dim must be a valid dimension");
90 endif
91 sz(dim) = n;
92
93 ns = length (subs);
94 ## Sort indices.
95 [subs, idx] = sort (subs(:));
96 ## Identify runs.
97 jdx = find (subs(1:ns-1) != subs(2:ns));
98 jdx = [jdx; ns];
99 ## Collect common slices.
100 szc = num2cell (sz);
101 szc{dim} = diff ([0; jdx]);
102 subsc = {':'}(ones (1, length (sz)));
103 subsc{dim} = idx;
104 val = mat2cell (val(subsc{:}), szc{:});
105 ## Apply reductions. Special case min, max.
106 if (func == @min || func == @max)
107 val = cellfun (func, val, {[]}, {dim}, "uniformoutput", false);
108 else
109 val = cellfun (func, val, {dim}, "uniformoutput", false);
110 endif
111 subs = subs(jdx);
112
113 ## Concatenate reduced slices.
114 val = cat (dim, val{:});
115
116 ## Construct matrix of fillvals.
117 if (fillval == 0)
118 A = zeros (sz, class (val));
119 else
120 A = repmat (fillval, sz);
121 endif
122
123 ## Set the reduced values.
124 subsc{dim} = subs;
125 A(subsc{:}) = val;
126
127 endfunction
128
129 %%test accumdim vs. accumarray
130
131 %!shared a
132 %! a = rand (5, 5, 5);
133
134 %!assert (accumdim ([1;3;1;3;3], a)(:,2,3), accumarray ([1;3;1;3;3], a(:,2,3)))
135 %!assert (accumdim ([2;3;2;2;2], a, 2, 4)(4,:,2), accumarray ([2;3;2;2;2], a(4,:,2), [1,4]))
136 %!assert (accumdim ([2;3;2;1;2], a, 3, 3, @min)(1,5,:), accumarray ([2;3;2;1;2], a(1,5,:), [1,1,3], @min))
137 %!assert (accumdim ([1;3;2;2;1], a, 2, 3, @median)(4,:,5), accumarray ([1;3;2;2;1], a(4,:,5), [1,3], @median))