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