accumarray

 Example 

 Create a -by- vector and sum values for repeated -D subscripts:
 val = :;
 subs = [; ; ; ; ]
 subs =

 A = accumarray(subs, val)
 A =
           % A() = val() =
           % A() = val()+val() = + =
             % A() =
           % A() = val()+val() = + = 

 The order of the subscripts matters:
 val = :;
 subs=[ ;  ;  ;  ;  ;  ];
 B1 = accumarray(subs,val,[],@(x)sum(diff(x)))

 B1 =

          -          

     -               

 Example 

 Create a -by--by- array and sum values for repeated -D subscripts:
 val = :;
 subs = [  ;   ;   ;   ;   ];

 A = accumarray(subs, val)
 A(:,:,) =

 A(:,:,) =

 Example 

 Create a -by--by- array, and sum values natively:
 val = :;
 subs = [  ;   ;   ;   ;   ];

 A = accumarray(subs, int8(val), [], @(x) sum(x,'native'))
 A(:,:,) =

 A(:,:,) =

 class(A)
 ans =
     int8

 Example 

 Pass multiple subscript arguments in a cell array.

 Create a -element vector V:
 V = :;

 Create three -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:
 %        index    index  => V()+V() => A(,,)
 %          |         |
 rowsubs = [           ];
 colsubs = [           ];
 pagsubs = [           ];
 %                |
 %              index  => V() => A(,,)
 %
 % A(,,) = V() + V() =  +  =
 % A(,,) = V() = 

 Call accumarray, passing the subscript vectors in a cell array:
 A = accumarray({rowsubs colsubs pagsubs}, V)
 A(:,:,) =
                           % A(,,) is 

 A(:,:,) =

                         % A(,,) is 

 Example 

 Create an array with the max function, and fill all empty elements of that array with NaN:
 val = :;
 subs = [ ;  ;  ;  ;  ];

 A = accumarray(subs, val, [ ], @max, NaN)
 A =
       NaN   NaN   NaN
       NaN      NaN

 Example 

 Create a sparse matrix using the prod function:
 val = :;
 subs = [ ;  ;  ;  ;  ];

 A = accumarray(subs, val, [ ], @prod, , true)
 A =
    (,)
    (,)
    (,)          

 Example 

 Count the number of entries accumulated in each bin:
 val = ;
 subs = [ ;  ;  ;  ;  ];

 A = accumarray(subs, val, [ ])
 A =

 Example 

 Create a logical array that shows which bins will accumulate two or more values:
 val = :;
 subs = [ ;  ;  ;  ;  ];

 A = accumarray(subs, val, [ ], @(x) length(x) > )
 A =

 Example 

 Group values in a cell array:
 val = :;
 subs = [ ;  ;  ;  ;  ];

 A = accumarray(subs, val, [ ], @(x) {x})
 A =
     [       ]     []              []     []
     [2x1 double]     []    [2x1 double]     []

 A{}
 ans =

Examples