IND2RC - Variant of IND2SUB behaving nicely with single output.

Description
Syntax
Inputs
Output:
Remark
See also
Function implementation

Description

Output the x- and/or y- subscripts from linear index as does IND2SUB, but enable one output only.

Syntax

  ij = IND2RC(siz, ind);
  ij = IND2RC(siz, ind, flag);

Inputs

siz : dimensions of the input matrix; note that it can be reduced to its x-dimension only.

ind : vector or matrix of linear indices.

flag (optional) string specifying the subscript to be computed; either the row ('r') or the colum ('c') subscript alone will be returned; flag can also be set to 'rc' or 'cr' to return both subscripts concatenated in the order indicated by the letter sequence; default: flag='rc'.

Output:

ij : matrix of dimension (n,k), where n is the number of rows of the input ind variable, and k is equal to length(flag):

when length(flag)=1, ij is the list of row or column (depending on flag) subscripts corresponding to the linear indices present in ind for a matrix of size siz,
when length(flag)=2, ij concatenates both the row and column subscripts and the order of concatenation is indicated by the char sequence in flag.

Remark

This function is implemented to remedy the behaviour of IND2SUB(siz,ind) which, by default, returns ind when one output only is specified.

Function implementation

function ij = ind2rc(siz, ind, flag)

error(nargchk(1, 3, nargin, 'struct'));
error(nargoutchk(0, 1, nargout, 'struct'));

X = siz(1);

if nargin<3 || isempty(flag)
    flag = 'rc';
elseif ~(ischar(flag) && any(strcmpi(flag,{'row','col','r','c','rc','cr'})))
    error('ind2rc:errorinput', ...
        'flag must be any string among ''r'', ''c'', ''rc'' or  ''cr''')
end

ind2row = @(i) mod((i-1),X) + 1;
ind2col = @(i) floor((i-1) / X) + 1;

switch flag(1)
    case {'r','row'}
        ij = ind2row(ind);

    case {'c','col'}
        ij = ind2col(ind);
end

if length(flag)==2
    switch flag(2)
        case 'r'
            ij = cat(2,ij,ind2row(ind));

        case 'c'
            ij = cat(2,ij,ind2col(ind));
    end

end

end % end of ind2rc