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function C = subsasgn (C, S, A)
%SUBSASGN C(I,J) = A or C(I) = A; assign submatrix.
% C(I,J) = A assigns A into the C(I,J) submatrix of the GraphBLAS matrix
% C. A must be either a matrix of size length(I)-by-length(J), or a
% scalar. Note that C(I,J) = 0 differs from C(I,J) = sparse (0). The
% former places an explicit entry with value zero in all positions of
% C(I,J). The latter deletes all entries in C(I,J). With a built-in
% sparse matrix C, both statements delete all entries in C(I,J) since
% Built-in sparse matrices never include explicit zeros.
%
% Linear indexing is not fully yet supported. With a single index,
% C(I) = A, both C and A must be vectors, except for C(:) = A where A is
% a matrix and C is a vector.
%
% If M is a logical matrix, C (M) = x is an assignment via logical
% indexing, where C and M have the same size, and x(:) is either a vector
% of length nnz (M), or a scalar.
%
% C (M) = A (M), where the logical matrix M is used on both the sides of
% the assignment, is the same as C = GrB.subassign (C, M, A). If C and A
% (or M) are GraphBLAS matrices, C (M) = A (M) uses GraphBLAS via operator
% overloading. The statement C (M) = A (M) takes about twice the time as
% C = GrB.subassign (C, M, A), so the latter is preferred for best
% performance. However, both methods in GraphBLAS are many thousands of
% times faster than C (M) = A (M) using purely built-in sparse matrices C,
% M, and A, when the matrices are large.
%
% If I or J are very large colon notation expressions, then C(I,J) = A is
% not possible, because I and J are created as explicit lists first,
% before passing them to GraphBLAS. See GrB.subassign instead. See also
% the example with 'help GrB.extract'.
%
% Just as the built-in C(I,J) = A, the GraphBLAS assignment can change the
% size of C if the indices I and J extend past the current dimesions of C.
%
% See also GrB/subsref, GrB/subsindex, GrB.assign, GrB.subassign.
% SuiteSparse:GraphBLAS, Timothy A. Davis, (c) 2017-2022, All Rights Reserved.
% SPDX-License-Identifier: Apache-2.0
% FUTURE: add all forms of linear indexing.
if (~isequal (S.type, '()'))
error ('GrB:error', 'index type %s not supported', S.type) ;
end
if (isobject (C))
C = C.opaque ;
end
if (isobject (A))
A = A.opaque ;
end
ndims = length (S.subs) ;
if (ndims == 1)
% C (M) = A if M is logical, or C (I) = A otherwise
S = S.subs {1} ;
if (isobject (S))
S = S.opaque ;
end
if (isequal (gbtype (S), 'logical'))
% C (M) = A for logical assignment
[am, an] = gbsize (A) ;
if (am == 1 && an == 1)
% C (M) = scalar
C = GrB (gbsubassign (C, S, A)) ;
else
% C (M) = A where A is a vector
C = GrB (gblogassign (C, S, A)) ;
end
else
% C (I) = A
[cm, cn] = gbsize (C) ;
[I, whole] = gb_index (S) ;
if (cm == 1 || cn == 1)
% C (I) = A for a vector or scalar C
C = GrB (gbsubassign (C, I, A)) ;
else
if (whole)
[am, an] = gbsize (A) ;
if (am == 1 && an == 1)
% C (:) = scalar, the same as C (:,:) = scalar.
% C becomes an iso full matrix
C_empty = gbnew (cm, cn, gbtype (C)) ;
C = GrB (gbsubassign (C_empty, { }, { }, A)) ;
else
% C (:) = A for a matrix C and vector A
C = GrB (gbreshape (A, cm, cn, 'by column')) ;
end
else
% C (I) = A, general case not yet supported
error ('GrB:error', ...
'Except for C(:)=A, linear indexing not yet supported') ;
end
end
end
elseif (ndims == 2)
% C (I,J) = A where A is length(I)-by-length(J), or a scalar
C = GrB (gbsubassign (C, gb_index (S.subs {1}), gb_index (S.subs {2}), A)) ;
else
% sparse N-dimensional arrays for N > 2 will not be supported
error ('GrB:error', '%dD indexing not supported', ndims) ;
end
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