Find highest third of values in dateset?

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Peter Mills
Peter Mills 2018-1-12
编辑： Star Strider 2018-1-12
WaveHeight=[3 1 5 2 3.1 6 5.5 3 2.5];
We need to find the highest 1/3:
HighestThird=[6 5.5 5]
But what if we what a function that will calculate the mean of the heights 1/3 of WaveHeight with the length of WaveHeight being a variable which may be large?
Please see my comment in this linked post How to determine significant wave height from time series data in Matlab
E.g.
WaveHeight=randi(1000,1,1000);
HighestThird=
  1 个评论
Adam
Adam 2018-1-12
编辑：Adam 2018-1-12
"calculate the mean of the heights 1/3 of WaveHeight"
I don't understand what this means. What is it you want to take the mean of and what is it you want 1/3 of?
Since you are starting your own question here it makes sense to include your information here rather than reference a comment in another question with more information than this one. There is no guarantee that independent question (or the answer to which you replied) will not get deleted.

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Star Strider
Star Strider 2018-1-12
编辑：Star Strider 2018-1-12
One approach is to use the sort function:
WaveHeight=[3 1 5 2 3.1 6 5.5 3 2.5];
[Waves,Idx] = sort(WaveHeight, 'descend');
HighestThird = WaveHeight(Idx(1:fix(numel(Idx)/3)))
HighestThird =
6 5.5 5
also:
HighestThird = Waves(1:fix(numel(Idx)/3))
with the same result.

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