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function [I, whole] = gb_index (I)
%GB_INDEX helper function for subsref and subsasgn
% [I, whole] = gb_index (I) converts I into a cell array of built-in
% matrices or vectors containing integer indices, to access A(I).
%
% I = { }: this denotes A(:), accessing all rows or all columns.
% In this case, the parameter whole is returned as true.
%
% I = { list }: denotes A(list)
%
% I = { start,fini }: denotes A(start:fini), without forming
% the explicit list start:fini.
%
% I = { start,inc,fini }: denotes A(start:inc:fini), without forming
% the explicit list start:inc:fini.
%
% The input I can be a GraphBLAS matrix (as an object or its opaque
% struct). In this case, it is wrapped in a cell, I = {gb_index1(I)},
% but kept as 1-based indices (they are later translated to 0-based).
%
% If the input is already a cell array, then it is already in one of the
% above forms. Any member of the cell array that is a GraphBLAS matrix or
% struct is converted into an index list, with gb_index1(I{k}).
%
% The subsref and subsasgn methods are passed the string I = ':'. This is
% converted into I = { }.
%
% If I is a built-in matrix or vector (not a cell array), then it is
% wrapped in a cell array, { I }, to denote A(I).
% SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2022, All Rights Reserved.
% SPDX-License-Identifier: Apache-2.0
whole = false ;
if (isobject (I))
% C (I) where I is a GraphBLAS matrix/vector of integer indices
I = I.opaque ;
I = { (gb_index1 (I)) } ;
elseif (isstruct (I))
% C (I) where I is the opaque struct of a GrB matrix/vector
I = { (gb_index1 (I)) } ;
elseif (iscell (I))
% The index I already appears as a cell, for the usage
% C ({ }), C ({ I }), C ({start,fini}), or C ({start,inc,fini}).
len = length (I) ;
if (len > 3)
error ('GrB:error', 'invalid indexing: usage is A ({start,inc,fini})') ;
elseif (len == 0)
% C ({ })
whole = true ;
else
% C ({ I }), C ({start,fini}), or C ({start,inc,fini})
for k = 1:length(I)
K = I {k} ;
if (isobject (K))
% C ({ ..., K, ... }) where K is a GraphBLAS object
K = K.opaque ;
end
if (isstruct (K))
% C ({ ..., K, ... }) where I is a GraphBLAS struct
I {k} = gb_index1 (K) ;
end
end
end
elseif (ischar (I) && isequal (I, ':'))
% C (:)
I = { } ;
whole = true ;
else
% C (I) where I is a built-in matrix/vector of integer indices
I = { I } ;
end
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