Inserting multiple rows into matrix, shifting existing rows - matlab

Question

Question:
I'm looking for the most efficient way to insert multiple rows R into a matrix M before specified rows I, while shifting existing rows down.
Example:
M = [1 1 1 1;
2 2 2 2;
3 3 3 3;
4 4 4 4;
5 5 5 5];
I = [1 3 3 5];
R = [-6 -6 -6 -6;
-7 -7 -7 -7;
-8 -8 -8 -8
-9 -9 -9 -9];
The result should be the matrix:
[-6 -6 -6 -6
1 1 1 1
2 2 2 2
-7 -7 -7 -7
-8 -8 -8 -8
3 3 3 3
4 4 4 4
-9 -9 -9 -9
5 5 5 5]

Answer 1

This functionality is available on the file exchange. What it essentially does is:
ind = [1:size(M, 1) I-1];
[~, ind] = sort(ind);
MR = [M; R];
MR = MR(ind,:);

Answer 2

The following will work, but I think only if the indices in I are sorted in increasing order (if not, you can always add some sorting steps first). In any case, I would test it with "real" data:
[m,n] = size(M);
l = length(I);
MM = zeros(m+l,n);
MM(I+(1:l)-1,:) = R; % I+(1:l)-1 are the row indices of the final matrix in which to insert the the rows of R
MM(~ismember(1:(l+m),I+(1:l)-1),:) = M; % ~ismember(...) are the other row indices (using logical indexing)
This gives:
>> MM
MM =
-6 -6 -6 -6
1 1 1 1
2 2 2 2
-7 -7 -7 -7
-8 -8 -8 -8
3 3 3 3
4 4 4 4
-9 -9 -9 -9
5 5 5 5

Answer 3

This could be one approach -
R_rowind = cumsum([I(1) diff(I)+1]) %// Row indices where rows from R are
%// to be inserted in the output matrix
rowidx_arr = 1:size(M,1)+size(R,1) %// array of [1 : number_of_rows_in_output]
out(setdiff(rowidx_arr,R_rowind),:) = M %// Insert rows from M into output array
out(R_rowind,:) = R %// Insert rows from R into output array
Please note that for inserting rows from M into output array, you can this bsxfun based alternative approach as well -
out(all(bsxfun(#ne,rowidx_arr,R_rowind'),1),:) = M