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回复 #7 JulianChin 的帖子
function [varargout] = accumarray(varargin)
% ACCUMARRAY Construct an array by accumulation.
% A = ACCUMARRAY(SUBS,VAL) creates an array A by accumulating elements of the
% vector VAL using the subscripts in SUBS. Each row of the M-by-N matrix
% SUBS defines an N-dimensional subscript into the output A. Each element of
% VAL has a corresponding row in SUBS. ACCUMARRAY collects all elements of
% VAL that correspond to identical subscripts in SUBS, sums those values, and
% stores the result in the element of A corresponding to the subscript.
% Elements of A that are not referred to by any row of SUBS contain zero.
%
% SUBS must contain positive integers. If SUBS is a nonempty matrix with N>1
% columns, then A is a N-dimensional array of size MAX(SUBS,[],1). If SUBS is
% empty with N>1 columns, then A is an N-dimensional empty array with size
% 0-by-0-by-...-by-0. SUBS may also be a column vector, and A is then also a
% column vector. In this case, A has length MAX(SUBS,[],1) when SUBS is
% nonempty, or length zero when SUBS is empty.
%
% SUBS may also be a cell vector with one or more elements, each a vector of
% positive integers. All of the vectors must have the same length. In this
% case, SUBS is treated as if the vectors formed columns of a subscript matrix.
%
% VAL must be a numeric, logical, or character vector with the same length
% as the number of rows in SUBS. VAL may also be a scalar whose value is
% repeated for all the rows of SUBS.
%
% ACCUMARRAY sums values from VAL using the default behavior of SUM.
%
% A = ACCUMARRAY(SUBS,VAL,SZ) creates an array A with size SZ, where SZ is a
% vector of positive integers. If SUBS is nonempty with N>1 columns, then SZ
% must have N elements, where ALL(SZ >= MAX(SUBS,[],1)). If SUBS is a nonempty
% column vector, then SZ must be [M 1] where M >= MAX(SUBS). Specify SZ as
% [] for the default behavior.
%
% A = ACCUMARRAY(SUBS,VAL,SZ,FUN) applies the function FUN to each subset of
% elements of VAL. FUN is a function that accepts a column vector and returns
% a numeric, logical, or char scalar, or a scalar cell. A has the same class
% as the values returned by FUN. FUN is @SUM by default. Specify FUN as []
% for the default behavior.
%
% Note: If the subscripts in SUBS are not sorted, FUN should not depend on the
% order of the values in its input data.
%
% A = ACCUMARRAY(SUBS,VAL,SZ,FUN,FILLVAL) puts the scalar value FILLVAL in
% elements of A that are not referred to by any row of SUBS. For example, if
% SUBS is empty, then A is REPMAT(FILLVAL,SZ). FILLVAL and the values returned
% by FUN must have the same class.
%
% A = ACCUMARRAY(SUBS,VAL,SZ,FUN,FILLVAL,ISSPARSE) creates an array A that is
% sparse if the logical scalar ISSPARSE is true, or full if ISSPARSE is false.
% A is full by default. FILLVAL must be zero or [] if ISSPARSE is true. VAL
% and the output of FUN must be double if ISSPARSE is true.
%
% Examples:
%
% Create a 5-by-1 vector, summing values for repeated 1-D subscripts:
% subs = [1; 2; 4; 2; 4];
% A = accumarray(subs, 101:105)
%
% Create a 2-by-3-by-2 array, summing values for repeated 3-D subscripts:
% subs = [1 1 1; 2 1 2; 2 3 2; 2 1 2; 2 3 2];
% A = accumarray(subs, 101:105)
%
% Create a 2-by-3-by-2 array, summing values natively:
% subs = [1 1 1; 2 1 2; 2 3 2; 2 1 2; 2 3 2];
% A = accumarray(subs, int8(101:105), [], @(x) sum(x,'native'))
% class(A)
%
% Create an array using MAX, and fill empty elements with NaN:
% subs = [1 1; 2 1; 2 3; 2 1; 2 3];
% A = accumarray(subs, 101:105, [2 4], @max, NaN)
%
% Create a sparse matrix using PROD:
% subs = [1 1; 2 1; 2 3; 2 1; 2 3];
% A = accumarray(subs, 101:105, [2 4], @prod, 0, true)
%
% Count the number of subscripts for each bin:
% subs = [1 1; 2 1; 2 3; 2 1; 2 3];
% A = accumarray(subs, 1, [2 4])
%
% Create a logical array indicating bins with two or more values:
% subs = [1 1; 2 1; 2 3; 2 1; 2 3];
% A = accumarray(subs, 101:105, [2 4], @(x) length(x)>1)
%
% Group values in a cell array:
% subs = [1 1; 2 1; 2 3; 2 1; 2 3];
% A = accumarray(subs, 101:105, [2 4], @(x) {x})
% A{2}
%
% See also FULL, SPARSE, SUM, FUNCTION_HANDLE.
% Copyright 1984-2005 The MathWorks, Inc.
% $Revision: 1.1.6.7 $ $Date: 2005/06/21 19:28:18 $
% Built-in function.
if nargout == 0
builtin('accumarray', varargin{:});
else
[varargout{1:nargout}] = builtin('accumarray', varargin{:});
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发表于 2007-6-27 18:11
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发表于 2007-6-27 19:09
