Nested for loops problem

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Jason Melody
Jason Melody 2017-10-29
评论： Walter Roberson 2017-10-30
Hi all,
Current problem: I have a 6 x 2 matrix, which looks like this:
5 0
3 0
8 2
1 2
3 2
2 2
I want to use a nested for loop with if statements to say "if 0 extract the number in the row beside" and "if 2 extract the number beside", so that I have two sets of data extracted from row 1 based on row 2's values.
Any solutions and in depth explanations especially would be great as need to get my head around these mock questions before an exam in two weeks. Thanks,
Jason.
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Guillaume
Guillaume 2017-10-30
I agree with Geoff. From the vague description of the desired result, I don't see the need for even one for loop and certainly can't see why you'd need nested loops. What would the inner loop iterate over?
If it's some homework problem that explicitly require the use of 2 loops, then we don't solve homework for you (that's called cheating and can get you excluded). We do provide help if you show that you made decent attempt at solving the problem and ask specific questions.
Walter Roberson
Walter Roberson 2017-10-30
I am not clear as to what "beside" here means, especially for ""if 0 extract the number in the row beside" as any given row may have up to two rows that are immediately beside the row.

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Guillaume
Guillaume 2017-10-30
Using no loop at all:
M = [5 0
3 0
8 2
1 2
3 2
2 2];
[~, ~, subs] = unique(M(:, 2))
result = accumarray(subs, M(:, 1), [], @(v) {v});
celldisp(result)

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