MATLAB: Matrix Question and row operations with a condition

basicconditionsmatrixrow operations.

Hello
If i have a matrix N x M, for example a matrix S:
     7 4 7
 S = 4 2 4
     0 2 -3
And i need to calculate for each row the average number. BUT there are some conditions!
1. If there is only one number, the final scalar = that number.
2. If there is more than 1 number, the average number is find by removing the lowest element in the vector and calculating the average number from the rest. The last condition: (HERE I AM HAVING TROUBLE)
3. IF ANY ELEMENT IN A ROW IS = -3 THEN THE FINAL SCALAR IS = -3. REGARDLESS OF THE OTHER 3 CONDITIONS.
My code in matlab is as follows (and it Works for the first to conditions):
    [N M] = size(S);
    i = 1:N;
    % The logical vector to include the data:
    logvec = true(size(S, 1), 1);
    % The three ways to calculate the final scalar:
    if M == 1
        logvec  = S(i,M);
    elseif M > 1
        logvec  = (sum(S')-min(S'))/(M-1);
    elseif M == -3            <--------Here is my problem!
       logvec  = -3;          <--------Here is my problem!
    end
    % Display of the Final scalar:
    gradesFinal = (logvec ');
    end
Can someone please help me out with the last condition? It's obvious that the first to rows in the matrix S, gives: 7 and 4, but the last row should give -3. Because of the last "condition".
(Also i am a new user to matlab, only 10 days of programming 😀 Yaaay!! ) Thanks!

Best Answer

You could avoid the for loop and use the power of MATLAB's indexing :
S = [7,4,7;4,2,4;0,2,-3;0,2,0];
Xn = S>0; % Or whatever your definition of "number" is.
X3 = any(S==-3,2);
X1 = ~X3 & sum(Xn,2)==1;
X2 = ~X3 & sum(Xn,2)>1;
M(X1,1) = S(bsxfun(@and,X1,Xn));
M(X2,1) = (sum(S(X2,:),2)-min(S(X2,:),[],2)) / (size(S,2)-1);
M(X3,1) = -3;
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