How to get the three maximum values from a vector

Hi, I want to know an efficient way of getting the three maximum values of a vector. Here is the whole question.

First I have a binary row vector of size n^2. This whole string can be split into substrings to form a matrix of order nxn. Then I sum the values of each column and it gives me a vector of size n of integers. for example, the string

0 0 1 0 1 0 - 0 0 0 1 1 1 -1 1 0 0 1 0 - 1 0 0 0 0 0 - 1 1 1 1 1 0

I used the next code to do the sum described above

for i=1:5
     suma=0;j=i;
     while(j<=5*5)
         suma=prueba(j)+suma;
         j=j+5;
     end
     vectorExito(i)=suma;
end

The vectorExito must be (3 2 2 2 4 1). I want to create a vector which has 1's in the positions that contains the three maximum values, otherwise 0's.

In this case I want the vector (1 1 1 1 1 0 ). Other example, if vectorExito is (2 3 4 4 5 1) then I want the vector (0 1 1 1 1 0). Other If vectorexito is (5 5 5 4 4 3) then the vector I want is ( 1 1 1 1 1 1).

How do I get the final binary vector given some vectorExito?

[Image Analyst]

You have 6 groups of five 0 or 1 values, so how can you group that into a 5x5 square array?

Answer 1

[Azzi Abdelmalek]

v=[5 2 4 4 1];
c=[0 0 unique(sort(v))];
res=zeros(1,length(v));
res(find(ismember(v,c(end-2:end))))=1

[cesar alvarez]

Hi, Im new working with matlab and I tried your code and it worked well. But I got a few questions, why do u use find in the 4th row instead of just assigning the values like this res=ismember(v,c(end-2:end))?, also why the two zeros before the word function unique? Thanks for your answer, I really appreciate that.

[Azzi Abdelmalek]

 ismember(v,c(end-2:end))=

 1     1     1     1     0

%what I need is the index corresponding to the true values

find(ismember(v,c(end-2:end)))=
   1     2     3     4

% why [0 0 ?

in case

v=[2 2 2 2 2]

 unique(sort(v))=2

then I can't compute c(end-2:end)

Answer 2

[Matt Fig]

% Your string:
s = '0 0 1 0 1 0 - 0 0 0 1 1 1 - 1 1 0 0 1 0 - 1 0 0 0 0 0 - 1 1 1 1 1 0';  
v = sum(str2num(strrep(s,'-',';'))); % vectorExito
idx = unique(v);
idx = ismember(v,idx(end-2:end))

Answer 3

[Image Analyst]

Try this:

% Generate sample data.
prueba = [0 0 1 0 1 0 0 0 0 1 1 1 1 1 0 0 1 0 1 0 0 0 0 0 1 1 1 1 1 0]

% Reshape into a 5 row by 6 column array.
m5x6 = reshape(prueba, [6 5])'

% Sum columns.
vectorExito = sum(m5x6)

% Sort in descneding order to find the highest values.
[sortedValues sortedIndexes] = sort(vectorExito, 'descend')
% Option below (depends on how you define the "third highest value"):
% sortedValues = fliplr(unique(sortedValues))

% Create the logical (boolean) output vector that is wanted.
% First get the third highest value.
thirdHighestValue = sortedValues(3);
wantedVector = vectorExito >= thirdHighestValue

Results:

prueba =
  Columns 1 through 14
     0     0     1     0     1     0     0     0     0     1     1     1     1     1
  Columns 15 through 28
     0     0     1     0     1     0     0     0     0     0     1     1     1     1
  Columns 29 through 30
     1     0
m5x6 =
     0     0     1     0     1     0
     0     0     0     1     1     1
     1     1     0     0     1     0
     1     0     0     0     0     0
     1     1     1     1     1     0
vectorExito =
     3     2     2     2     4     1
sortedValues =
     4     3     2     2     2     1
sortedIndexes =
     5     1     2     3     4     6
wantedVector =
     1     1     1     1     1     0