1 Example 1
2
3
4 Create a 5-by-1 vector and sum values for repeated 1-D subscripts:
5 val = 101:105;
6 subs = [1; 2; 4; 2; 4]
7 subs =
8 1
9 2
10 4
11 2
12 4
13
14 A = accumarray(subs, val)
15 A =
16 101 % A(1) = val(1) = 101
17 206 % A(2) = val(2)+val(4) = 102+104 = 206
18 0 % A(3) = 0
19 208 % A(4) = val(3)+val(5) = 103+105 = 208
20
21
22 0 0
23 0 0 0 0
24 0 0 0 0
25 2 0 0 0
26
27
28 The order of the subscripts matters:
29 val = 101:106;
30 subs=[1 2; 3 1; 1 2; 4 4; 4 1; 4 1];
31 B1 = accumarray(subs,val,[],@(x)sum(diff(x)))
32
33 B1 =
34
35 0 -2 0 0
36 0 0 0 0
37 0 0 0 0
38 -1 0 0 0
39
40
41 Example 3
42
43
44 Create a 2-by-3-by-2 array and sum values for repeated 3-D subscripts:
45 val = 101:105;
46 subs = [1 1 1; 2 1 2; 2 3 2; 2 1 2; 2 3 2];
47
48 A = accumarray(subs, val)
49 A(:,:,1) =
50 101 0 0
51 0 0 0
52 A(:,:,2) =
53 0 0 0
54 206 0 208
55
56 Example 4
57
58
59 Create a 2-by-3-by-2 array, and sum values natively:
60 val = 101:105;
61 subs = [1 1 1; 2 1 2; 2 3 2; 2 1 2; 2 3 2];
62
63 A = accumarray(subs, int8(val), [], @(x) sum(x,'native'))
64 A(:,:,1) =
65 101 0 0
66 0 0 0
67 A(:,:,2) =
68 0 0 0
69 127 0 127
70
71 class(A)
72 ans =
73 int8
74
75 Example 5
76
77
78 Pass multiple subscript arguments in a cell array.
79
80 Create a 12-element vector V:
81 V = 101:112;
82
83
84
85 Create three 12-element vectors, one for each dimension of the resulting array A. Note how the indices of these vectors determine which elements of V are accumulated in A:
86 % index 1 index 6 => V(1)+V(6) => A(1,3,1)
87 % | |
88 rowsubs = [1 3 3 2 3 1 2 2 3 3 1 2];
89 colsubs = [3 4 2 1 4 3 4 2 2 4 3 4];
90 pagsubs = [1 1 2 2 1 1 2 1 1 1 2 2];
91 % |
92 % index 4 => V(4) => A(2,1,2)
93 %
94 % A(1,3,1) = V(1) + V(6) = 101 + 106 = 207
95 % A(2,1,2) = V(4) = 104
96
97
98 Call accumarray, passing the subscript vectors in a cell array:
99 A = accumarray({rowsubs colsubs pagsubs}, V)
100 A(:,:,1) =
101 0 0 207 0 % A(1,3,1) is 207
102 0 108 0 0
103 0 109 0 317
104 A(:,:,2) =
105 0 0 111 0
106 104 0 0 219 % A(2,1,2) is 104
107 0 103 0 0
108
109 Example 6
110
111
112 Create an array with the max function, and fill all empty elements of that array with NaN:
113 val = 101:105;
114 subs = [1 1; 2 1; 2 3; 2 1; 2 3];
115
116 A = accumarray(subs, val, [2 4], @max, NaN)
117 A =
118 101 NaN NaN NaN
119 104 NaN 105 NaN
120
121 Example 7
122
123
124 Create a sparse matrix using the prod function:
125 val = 101:105;
126 subs = [1 1; 2 1; 2 3; 2 1; 2 3];
127
128 A = accumarray(subs, val, [2 4], @prod, 0, true)
129 A =
130 (1,1) 101
131 (2,1) 10608
132 (2,3) 10815
133
134
135 Example 8
136
137
138 Count the number of entries accumulated in each bin:
139 val = 1;
140 subs = [1 1; 2 1; 2 3; 2 1; 2 3];
141
142 A = accumarray(subs, val, [2 4])
143 A =
144 1 0 0 0
145 2 0 2 0
146
147 Example 9
148
149
150 Create a logical array that shows which bins will accumulate two or more values:
151 val = 101:105;
152 subs = [1 1; 2 1; 2 3; 2 1; 2 3];
153
154 A = accumarray(subs, val, [2 4], @(x) length(x) > 1)
155 A =
156 0 0 0 0
157 1 0 1 0
158
159 Example 10
160
161
162 Group values in a cell array:
163 val = 101:105;
164 subs = [1 1; 2 1; 2 3; 2 1; 2 3];
165
166 A = accumarray(subs, val, [2 4], @(x) {x})
167 A =
168 [ 101] [] [] []
169 [2x1 double] [] [2x1 double] []
170
171 A{2}
172 ans =
173 104
174 102
