Help with looping variables

Hi guys!

I have run into problems when I try to make a loop create variables and I am not very advanced in matlab. Here is what I am trying to do:

I have a .csv-file containing columns with data, each called test1, test2 and so forth. For each column, I am trying to create a variable in matlab - something like:

for i = 1:10 
test(i) = csvvariable(:,i)
end

What I have done so far is manually creating a variable for each column in the .csv-file:

   rfdtest = csvread('Hamstring.csv', 8, 1);

test1 = rfdtest(:,1);
    if test1(1)>0
        test1=[0;test1]
    end
test2 = rfdtest(:,2);
     if test2(1)>0
        test2=[0;test2]
    end
test3 = rfdtest(:,3);
    if test3(1)>0
        test3=[0;test3]
    end
test4 = rfdtest(:,4);
    if test4(1)>0
        test4=[0;test4]
    end
test5 = rfdtest(:,5);
    if test5(1)>0
        test5=[0;test5]
    end
test6 = rfdtest(:,6);
    if test6(1)>0
        test6=[0;test6]
    end
test7 = rfdtest(:,7);
    if test7(1)>0
        test7=[0;test7]
    end
test8 = rfdtest(:,8);
    if test8(1)>0
        test8=[0;test8]
    end
test9 = rfdtest(:,9);
    if test9(1)>0
        test9=[0;test9]
    end
test10 = rfdtest(:,10);
    if test10(1)>0
        test10=[0;test10]
    end

Later, I am going to do some calculations on each column, so this method will result in a lot of code.

Thanks in advance and feel free to ask for additional details!

[Stephen23]

"I have run into problems when I try to make a loop create variables and I am not very advanced in matlab."

Magically accessing variable names is one way that beginners force themselves into writing slow, complex, buggy code that is hard to debug. Read this to know why:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

The simplest alternative is to use indexing to access you data, which is neat, simple, easy to debug, and highly efficient (unlike what you are trying to do). All of the data are already trivially accessible using indexing from the variable csvvariable. Note that splitting up the data (pointlessly) duplicates it in memory.

"What I have done so far is manually creating a variable for each column in the .csv-file:"

Seems complex. Copy-and-pasting code is a sign that you are doing something wrong. Instead of copy-and-pasting code, get the computer to do it for you using loops and indexing. Copy-and-pasting causes bugs (e.g. your code repeating exactly the same test) and bloats the code.

[Mikkel Eskildsen]

I was very aware my approach was definitely not the way to go, I just had to do it for myself to be able to gain an overview of what i'm trying to do.

I will look into indexing and see if I can figure out the way to do it, and otherwise come back for help. Thank you for your response!

Answer 1

[Image Analyst]

Unfortunately you've probably delayed any answer by not attaching 'Hamstring.csv', and not reading this link to learn how to format your code.

Also, read this

All of your "if" statements are the same

if test2(1)>0

but you have test3, test4, etc. so shouldn't you also change the if tests?

[Mikkel Eskildsen]

Sorry! I have attached the csv-file now and reformatted the code. Also, the if statements were an obvious typo, I forgot to change each to the corresponding test variable - thank you.

[Image Analyst]

You Accepted the answer, so did fixing the typos fix it? Is everything working now?

[Mikkel Eskildsen]

It sure did fix a mistake I made, but I didn't realize that you can only accept one answer until afterwards where I couldn't undo it. I still face my problem - which is now, how to efficiently access my data without having to manually create variables for each column and do my calculations on each one.

The other editor "Stephen Cobeldick" suggested using indexing to access my data, but after reading a few articles I think I need some suggestions on how I could proceed. Some additional info:

Each test-column in "Hamstring.csv" is data from Rate of Force Development Tests(RFD). My final product would be a GUI in matlab that reads the selected csv-file after browsing, and then a button, "Analyze", that performs a number of calculations on each test(column). The results is then shown to the user.

If you need more info do ask me, and I apologize for the confusion caused by not reading into posting questions beforehand!

Edit: I made the GUI already, so that is not not my issue. Also, I just found the unaccept button.

[Mikkel Eskildsen]

I might have figured it out by using cell arrays:

rfdtest = csvread('Hamstring.csv', 8, 1);

for i=1:10
    T{i} = rfdtest(:,i);
end

Would this be simple and efficient to proceed with?

[Image Analyst]

No. Cell arrays are not efficient. I don't know why you'd want or need a cell array. Isn't rfdtest a 2-D double matrix? Why can't you just deal with that? Or if you want to extract one column at a time and process it, then just do this:

for k = 1 : 10
    thisColumn = rfdtest(:, k);
    % Now do something with thisColumn.  Probably no need to store it for use after the loop.
end

[Mikkel Eskildsen]

I did it after reading the accepted answer in this topic. In the loop I am going to add a zero in the beginning of all columns where zero isn't the first element, which is why the columns will have different sizes. But if that it not going to have any influence, I will try using your example.

[Mikkel Eskildsen]

I made it work with the simple loop you proposed. Thank you for your help!

[Image Analyst]

You can do

for k = 1 : 10
    thisColumn = rfdtest(:, k);
    if thisColumn(1) ~= 0
        thisColumn = [0; thisColumn];
    end
    % Now do something with thisColumn.  Probably no need to store it for use after the loop.
end

Again, no inefficient cell arrays needed unless for some reason you need to keep/store all the individual columns after the loop ends, which you haven't shown any need for.

If you do, you'd to this:

ca = cell(10, 1); % Preallocate a cell array
for k = 1 : 10
    thisColumn = rfdtest(:, k);
    if thisColumn(1) ~= 0
        thisColumn = [0; thisColumn];
    end
    ca{k} = thisColumn; % Store in a cell array.
    % Now do something with thisColumn.
end