Finding the second smallest value in each column of an array?

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Jason
Jason 2011-8-7
This is probably very simple. I have an array of size, say 10 by 30. In each column, there is definitely an element with a value of 0, the rest of the nine: values > 0. Now, I want a row vector containing the second smallest values from each column of the original array.
Any idea? If I were to use min(array), I would get a row vector with all 0's. Maybe I have to use bubble sorting?

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回答（3 个）

Jan
Jan 2011-8-7
Sorting is a good idea:
X = rand(10, 10);
Xs = sort(X);
min2nd = Xs(2, :);
This is not very efficient, but most likely the fastest Matlab method.
Walter Roberson
Walter Roberson 2011-8-7
t = array;
t(t==0) = inf;
min(t)
Pierre
Pierre 2011-8-7
You could simply take advantage of Bruno Luong's Min/Max selection implemented in MEX. AFAIK they implement Hoare's selection algorithm (which is a deviation of quicksort).

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