MATLAB: 2.1 –> A problem with an Nx3 matrix.

conditionsdataloadmatrix

Hello !
(You can read the attached file, under section: 2.1 DATA LOAD FUNCTION , thanks.)
I have written the following code:
function data = dataLoad(filename) %A function that reads a datafile and returns an nx3 matrix, with the acceptet rows. % also returning error messages. %the name of the file that i will use: tgb.csv. data = readtable('tgb.csv');
% for loop that chekcs if the temperature is between 10 og 60. if (10<(tgb(:,1)); disp('Temperature must be between 10 and 60'); elseif (tgb(:,1)<60); continue; end continue; % for loop that checks if the growthRate is a positive number. for (tgb(:,2) < 0); disp('Growth rate must be postive'); continue; end % for loop that identifies the bacteria. for (tgb(:,3) > 4) error('invalid number. The number must be between 1 and 4'); case tgb(:,3) of 1 do return('Salmonella enterica'); of 2 do return('Bacillus cereus'); of 3 do return('Listeria'); of 4 do return('Brochothrix thermosphacta'); continue; end
—————————————————————————————-
That does not Work for me! First this is my 7 matlab problem, and i am new user… So please be patient 🙂
I have to figure out: 1. how to call the matrix, and display the rows that are "true" in a N x 3 matrix. 2. how to make the conditions for ROWS instead of COLOMNS. (That is what i have done) –> Is it something like:
for i = 1:length(data(:,1))-1 % loop gennem alle rækker. if sum(data(i,:))>sum(data(i+1,:)); end end elseif CONDITION
    elseif CONDITION
end ???
???
If someone could help me find an easier way or help me with the solution, it will be fantastic,
NOTICE: I only need help with the 2.1 section in the attached file. I have also attached my csv file.
Thanks for your time!

Best Answer

Deleting rows or columns is done by an index operation. Set that row (or column) or rows, etc., to []. For example:
A = magic(4)
A =
  16     2     3    13
   5    11    10     8
   9     7     6    12
   4    14    15     1
Lets delete the first and third rows.
A([1 3],:) = []
A =
   5    11    10     8
   4    14    15     1
As you can see, only the 2nd and 4th rows remain. Column deletion works the same way, by column indexing, setting them to empty.
As for your other questions, I have no idea what you mean by how to "call the matrix". I might try, "Here matrix, here boy". It works for my dog anyway.
I also do not know exactly what you mean by "Displaying the rows that are true". To find any row of M that has any value that exceeds 4, just do a test.
A = [1,2,3:4,5,6:7,8,9;1,2,3;2,3,4];
rowind = any(A > 4,2)
rowind =
   0
   1
   1
   0
   0
As you can see, this returns a boolean vector, true or false for any rows that met the criterion.
Now we can zap those rows away via one of two methods. We can use find to find the index of the rows for deletion, or we can just index directly using the boolean vector. So either of these following forms will work:
A(find(rowind),:) = [];
A(rowind,:) = [];
Sometimes you will need to use the actual indices of those rows for other purposes, so you might use the find operation. Either case will result in the matrix:
A
A =
   1     2     3
   1     2     3
   2     3     4
Finally, I would point out that nothing I did here used or needed an explicit loop. This is MATLAB. Learn to use matrices and vectors.
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