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Build array from descriptive data without a loop

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Gabriel Stanley
Gabriel Stanley 2023-2-17
评论： Walter Roberson 2023-2-17
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
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采纳的回答

Walter Roberson
Walter Roberson 2023-2-17
Ran in:
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))
Array2 = 7×1
10 13 16 1000 1178 1356 1534
  2 个评论
Gabriel Stanley
Gabriel Stanley 2023-2-17
Kinda disappointed this hasn't ended up being significantly faster in my use-case, but thank you for providing an answer. I never would've thought to use arrayfun (or cellfun & the like) because I've gotten the impression they're generally slower than a loop.
Walter Roberson
Walter Roberson 2023-2-17
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.

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更多回答（1 个）

Kevin Holly
Kevin Holly 2023-2-17
Ran in:
Array1 = [10,3,3;1000,178,4];
Array2 = cumsum(Array1,2)
Array2 = 2×3
10 13 16 1000 1178 1182
  2 个评论
Walter Roberson
Walter Roberson 2023-2-17
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.

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