Question

I have a matrix:

mat = [  2009 3 ;
         2010 2 ] ;

I need to repeat the Col1 as per Col2. The solution at Repeat copies of array elements: Run-length decoding in MATLAB is helpful. However, my main problem is to then increment the years according, as in:

Ansmat = [  2009 3
            2010 3
            2011 3
            2010 2
            2011 2 ] ;

I want to avoid a for loop here. Thanks for your help! This would be a great help!

Answer 1

You can first replicate your matrix using my vectorized answer to the previous question:

>> mat = [2009 3; 2010 2];
>> index = zeros(1, sum(mat(:, 2)));
>> index([1; cumsum(mat(1:end-1, 2))+1]) = 1;
>> Ansmat = mat(cumsum(index), :)

Ansmat =

        2009           3
        2009           3
        2009           3
        2010           2
        2010           2

Next, you can create a column vector of offsets to add to the dates in the first column. Here’s how you can do this in a vectorized way.

>> offset = ones(size(Ansmat, 1), 1);
>> offset([1; cumsum(mat(1:end-1, 2))+1]) = [0; 1-mat(1:end-1, 2)];
>> Ansmat(:, 1) = Ansmat(:, 1)+cumsum(offset)

Ansmat =

        2009           3
        2010           3
        2011           3
        2010           2
        2011           2