Build array from descriptive data without a loop
3 views (last 30 days)
Show older comments
Gabriel Stanley
on 17 Feb 2023
Commented: Walter Roberson
on 17 Feb 2023
I want to go from
Array1 = [10,3,3;1000,178,4];
to
Array2 = [10;13;16;1000;1178;1356;1534];
without using
Idx2 = 1;
Array2 = zeros(sum(Array1(:,3)),1);
for Idx1 = 1:size(Array1,1)
Array2(Idx2:Idx2+Array1(Idx1,3)-1) = [Array1(Idx1,1),Array1(Idx1,1)+[1:Array1(Idx1,3)-1].*Array1(Idx1,2)];
Idx2 = Idx2+Array1(Idx1,3)-1;
end
Help?
0 Comments
Accepted Answer
Walter Roberson
on 17 Feb 2023
Array1 = [10,3,3;1000,178,4];
Array2 = cell2mat(arrayfun(@(Idx) Array1(Idx,1) + (0:Array1(Idx,3)-1).'*Array1(Idx,2), (1:size(Array1,1)).','uniform', 0))
2 Comments
Walter Roberson
on 17 Feb 2023
You didn't ask for performance, you asked for not using a loop. For most operations (but not all, not if you know the right obscure forms), arrayfun and cellfun are slower than looping.
If you were looking for performance, then your existing code could be tweeked to take advantage of cumsum() instead of calculating the indices each time, and you could use the calculation I used instead of using [original, colon expression] list constructor.
More Answers (1)
Kevin Holly
on 17 Feb 2023
Array1 = [10,3,3;1000,178,4];
Array2 = cumsum(Array1,2)
2 Comments
Walter Roberson
on 17 Feb 2023
Tthe third column is the number of elements to generate, with the difference being the second column, and the starting point being the first column.
See Also
Categories
Find more on Matrices and Arrays in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!