find the multiple max values
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I have a matrix
8 23 44 19
44 5 62 1
7 6 12 33
6 55 24 8
and I want to find 3 largest values(reserve duplicate matches),and then make the other be 0
just like
0 0 44 0
44 0 62 0
0 0 0 0
0 55 0 0
I have read some book ，but I still have no idea
help me plz
3 个评论
Aditya Verma
2020-6-16
Hello, could you please specify what you have tried until now, and in which part you are facing problem.
chung yen chang
2020-6-18
chung yen chang
2020-6-18
采纳的回答
madhan ravi
2020-6-16
编辑：madhan ravi
2020-6-16
MaX = maxk(matrix(:), 3);
Wanted = ismember(matrix, MaX) .* matrix
% for older versions
m = sort(matrix(:),'descend');
Wanted = ismember(matrix, m(1:3)) .* matrix
11 个评论
Aditya Verma
2020-6-16
While this works for the example provided by OP. This would not work for all cases.
madhan ravi
2020-6-16
Illustrate.
Aditya Verma
2020-6-16
Consider the following:
matrix = [8 23 46 19;
47 5 62 1 ;
7 6 12 33 ;
6 55 24 8];
[MaX, index] = maxk(matrix(:),4);
Wanted = zeros(size(matrix));
Wanted(index) = MaX
It gives the following output:
0 0 46 0
47 0 62 0
0 0 0 0
0 55 0 0
Which preserves four max values.
madhan ravi
2020-6-16
编辑：madhan ravi
2020-6-16
Isn’t that what the OP is looking for? Change 4 to 3.
Aditya Verma
2020-6-16
编辑：Aditya Verma
2020-6-16
OP mentioned: "I want to find 3 largest values(reserve duplicate matches),and then make the other be 0". If I understand correctly, it means that OP wants to preserve max three values, but preserve the duplicates. So, if my elements in matrix in descinding order are: 9, 9, 9, 8, 8, 7, 7, 3, 2, 0, -1, -1. Then all the 9s, 8s and 7s should persist, and rest all should be 0.
In the example I provided above, it is preserving max 4 values.
madhan ravi
2020-6-16
编辑：madhan ravi
2020-6-16
Yes, you’re right. Rectified.
chung yen chang
2020-6-18
编辑：chung yen chang
2020-6-18
madhan ravi
2020-6-18
编辑：madhan ravi
2020-6-18
Chung did you even see my answer with the second option even though I specifically mentioned for “older versions”. Come on!
chung yen chang
2020-6-18
madhan ravi
2020-6-18
In the command window just call the function
Matrix = randi(10,4); % an example
Wanted = Mx(Matrix)
% function definition
function Wanted = Mx(matrix) % save it as a separate file called Mx.m
... the Code
end
Stephen23
2020-6-18
Note that this answer does not "find 3 largest values" as the question requested:
>> matrix = [4,4,4;4,4,4;3,2,1]
matrix =
4 4 4
4 4 4
3 2 1
>> m = sort(matrix(:),'descend');
>> Wanted = ismember(matrix, m(1:3)) .* matrix
Wanted =
4 4 4
4 4 4
0 0 0
The problem is caused by the use of sort. See my answer for the correct solution.
更多回答（1 个）
Stephen23
2020-6-16
Where M is your matrix:
>> U = unique(M(:));
>> X = ismember(M,U(end-2:end));
>> M(~X) = 0
M =
0 0 44 0
44 0 62 0
0 0 0 0
0 55 0 0
3 个评论
chung yen chang
2020-6-18
"Thanks, bro this answer can work very well"
Note my answer actually gives the output that you asked for (unlike the answer that you accepted):
>> M = [4,4,4;4,4,4;3,2,1]
M =
4 4 4
4 4 4
3 2 1
>> U = unique(M(:));
>> X = ismember(M,U(end-2:end));
>> M(~X) = 0
M =
4 4 4
4 4 4
3 2 0
madhan ravi
2020-6-18
However maxk(...) gives the right answer xD, but i do agree the loophole.
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