Setting X as a column of a matrix

So I have another question: How do i tell MATLAB to go thru the matrix and take the second column of this and apply it to the if statement i have coded below:

   M = [1, 80.8 %A Matrix for the grades
       2, 79
       3, 87.4
       4, 74.2
       5, 82
       6, 85]
  %The following if, else if and else statement calculates the grades based
  %on the values of X.
  if X<60
    y = F
  elseif X>=60 & X<70
    y = D
  elseif X>=70 & X<80
    y = C
    elseif X>=80 & X<90
    y = B
  else
    y = A
  end

After I do that, I want it to output into a matrix like the one above, but with another column where the y will go.

Answer 1

[Matt Fig]

Use a FOR loop to loop over the rows of column 2. But you are going to want to define A,B,C,D,F or you will get errors. Unless you mean 'A','B','C','D','F'. And to store the values, assign each one to a position in an array.

for ii = 1:length(M)
       X = M(ii,2);  % Assign this value to X, each time through
       if X<60
           y = F;
       elseif X>=60 & X<70
           y = D;
       elseif X>=70 & X<80
           y = C;
       elseif X>=80 & X<90
           y = B;
       else
           y = A;
       end
       GR(ii) = y
   end

[Jonathon]

Well what I am looking for, to be more specific, is for it to take the values of column 2, assign a letter grade, and be able to print the resulting values into a new matrix.

[Matt Fig]

So did you try it? Like I said, you should use 'A' instead of A, 'B' instead of B...

M = [1, 80.8 %A Matrix for the grades
    2, 79
    3, 87.4
    4, 74.2
    5, 82
    6, 85]

for ii = 1:length(M)
       X = M(ii,2);  
       if X<60
           y = 'F';
       elseif X>=60 & X<70
           y = 'D';
       elseif X>=70 & X<80
           y = 'C';
       elseif X>=80 & X<90
           y = 'B';
       else
           y = 'A';
       end
       GR(ii) = y;
end

GR.'

[Jonathon]

Yeah I have, thanks I've gathered all I need.

Answer 2

[Matt Kindig]

You can also do this using logical indexing, which is a more "Matlab-y" way to do this problem...

y = repmat('A', size(M(:,1)));   %set default grade to 'A'
X = M(:,2);
%these various truth conditions assign letter grade appropriately
y(X<60) = 'F';
y(X>=60 & X<70) = 'D';
y(X>=70 & X<80) = 'C';
y(X>=80 & X<90)= 'B';

[Matt Fig]

See the OP's previous post for more info...

Answer 3

[Andrei Bobrov]

M = [1, 80.8 %A Matrix for the grades
2, 79
3, 87.4
4, 74.2
5, 82
6, 85];

x = cellstr(['F';('D':-1:'A')']); % OR x = ['F';('D':-1:'A')'];
[a,b] = histc(M(:,2),[-inf,(6:9)*10,inf]);
out = x(b);

OR

x = ['F';('D':-1:'A')'];
out = x(sum(bsxfun(@gt,M(:,2),[-inf,(6:9)*10,inf]),2));