matlab - vectorized array creation from a list of start/end indices

Question

I have a two-column matrix M that contains the start/end indices of a bunch of intervals:

startInd   EndInd
1          3
6          10
12         12
15         16

How can I generate a vector of all the interval indices:

v = [1 2 3 6 7 8 9 10 12 15 16];

I'm doing the above using loops, but I'm wondering if there's a more elegant vectorized solution?

v = [];
for i=1:size(M,1)
    v = [v M(i,1):M(i,2)];
end

Answer 1

Here's a vectorized solution I like to use for this particular problem, using the function cumsum:

v = zeros(1, max(endInd)+1);  % An array of zeroes
v(startInd) = 1;              % Place 1 at the starts of the intervals
v(endInd+1) = v(endInd+1)-1;  % Add -1 one index after the ends of the intervals
v = find(cumsum(v));          % Perform a cumulative sum and find the nonzero entries