Problem 36. Find relatively common elements in matrix rows

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Appears in Probability & Stats

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You want to find all elements that exist in greater than 50% of the rows in the matrix.
For example, given
 A =
     1 2 3 5
     9 2 5 9
     3 2 5 8
     1 2 1 5
     5 1 3 2
the answer would be the row vector
 [1  2  3  5]
since each of these appears three or more times in the rows of matrix A. Elements should be returned sorted ascending.
Note there is no guarantee that there are any such elements; if there are none, the routine should return the empty set. Also, the matrix might contain repeats, very large or very small numbers, or NaNs (though NaN should not be treated as a number to be returned in the output).

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Last Solution submitted on Feb 05, 2025

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Simon Thomas on 20 Nov 2017

This needs another test case.
Many would fail this:

%%
x = [1 1 1 1;2 3 4 5;3 6 7 8];
y_correct = [3];
assert(isequal(common_by_row(x),y_correct))

arsenic 陈 on 10 May 2021

https://blog.csdn.net/qq_44846756/article/details/116567963
i thought different

Dyuman Joshi on 25 Aug 2021

The test suit has been updated to check for miscellaneous cases and a reference solution is added.

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Problem 36. Find relatively common elements in matrix rows

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Problem 36. Find relatively common elements in matrix rows

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