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Identify the mode in each column and eliminate them

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Han
Han 2013-6-6
I am curious to see if the following could be done without loops.
I have a 7-by-N matrix with all integers. In each column of the matrix, there is one integer that appears 4 time (hence the most frequent integer).
This there any way to eliminate the most frequent integers in every column and to output the rest of the integers in a 3-by-N matrix without using loops?
Example: a = [1 1 2 2 2 2 3; 1 2 2 2 2 3 3; 2 2 2 2 3 3 3]';
Output should be [1 1 3; 1 3 3; 3 3 3]'
The order of numbers in each column could be randomized unlike in my example. Thank you very much and no this is not a homework problem.
  1 个评论
Han
Han 2013-6-7
Edit: I used number 1,2 and 3 just for my example. The integers could be different. There could be different "mode" numbers (the most frequent numbers) in different columns.

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采纳的回答

Andrei Bobrov
Andrei Bobrov 2013-6-6
编辑：Andrei Bobrov 2013-6-7
reshape(a(ismember(a,[1,3])),[],size(a,2));
or
hankel([1 1 3],[3 3 3]);
ADD
s = size(a);
b = ones(s);
idxl = fliplr(triu(b,1) + tril(b,diff(s))) > 0;
out = reshape(a(idxl),[],s(2));
  2 个评论
Han
Han 2013-6-7
Number 1,2 and 3 only appeared in my example. It does not mean they should be the ones you use in your code.

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更多回答（2 个）

Iain
Iain 2013-6-6
a = a';
out = reshape(a(a~=2),[],3)';
That will work for your example, but not necessarily what you're dealing with.
  1 个评论
Han
Han 2013-6-7
Number 1,2 and 3 only appeared in my example. It does not mean they should be the ones you use in your code.

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Roger Stafford
Roger Stafford 2013-6-7
Let 'a' be an array in which one element of each row is repeated the same number of times for all rows with no other element in each row occurring as often as this.
b = a.';
b = reshape(b(bsxfun(@ne,mode(b),b)),[],size(b,2)).';

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