Creating a string for loop.

Hi, I'm trying to simplify my code. Right now I have my code set up like this:

Percentageoftimein_mp =  sum(in_mp)/(length(in_mp))
Percentageoftimein_mb =  sum(in_mb)/(length(in_mb))
Percentageoftimein_mp =  sum(in_mp)/(length(in_mp))
Percentageoftimein_mcup =  sum(in_mcup)/(length(in_mcup))
Percentageoftimein_mclow =  sum(in_mclow)/(length(in_mclow))
Percentageoftimein_bof =  sum(in_bof)/(length(in_bof))
Percentageoftimein_mc = PercentageoftimeinMClow+PercentageoftimeinMCup ;

I feel like I should be able to simplify this into a loop then adding my last line after the loop like this:

	names ={'in_cob','in_mb','in_mp','in_mcup','in_mclow','in_bof'}
    for 1:length(names)
        Percentageoftime+names = sum(names)/(length(names))
    end
    Percentageoftimein_mc = PercentageoftimeinMClow+PercentageoftimeinMCup ;

But I keep getting this error when I try:

% File: plot_smolts.m Line: 91 Column: 9
% Invalid expression. Check for missing multiplication operator, missing or unbalanced delimiters, or other
% syntax error. To construct matrices, use brackets instead of parentheses.

Not sure how I should go about doing this.

[Stephen23]

"I'm trying to simplify my code"

Then you need to fix your data design first.

"Not sure how I should go about doing this."

Not with your current approach. Forcing meta-data into variable names is a path you do not want to go down:

https://www.mathworks.com/matlabcentral/discussions/tips/849901-tutorial-why-variables-should-not-be-named-dynamically-eval

All of your operations are exactly the same, so most likely you could place the data in two arrays (eg. table, cell, struct) and then apply that operation to that array. Also note that MATLAB already has a MEAN function, so rather than reinventing the wheel you should use that... if possible with all of the data in just two numeric arrays.

Answer 1

[Matt J]

Instead of separate variables, they should be struct fields,

in.mp=[1,2,3];
in.bof=[11,12,13],

in = struct with fields:
     mp: [1 2 3]
    bof: [11 12 13]

and so forth. Then you can produce a new struct with the percentages simply by doing,

Percentageoftime=structfun(@mean, in, 'uni',0)

Percentageoftime = struct with fields:
     mp: 2
    bof: 12

[Matt J]

You could also loop explicitly, instead of using structfun,

for field=["mp","bof"]
    
    Percentageoftime.(field) =  mean(in.(field));
    
end

[Sophie]

Hi, thank you for the response, but I'm slightly confused. I should have mentioned in my original post I'm quite new to coding/MATLAB so I've never seen a struct field before. I tried to look up info on it but I'm not sure I understand in this context.

What does the mean function do here? I'm also a little confused about how does the set up of the numbers in the struct field work? Sorry I'm not super quick at picking these things up. Thanks again!

[Sophie]

Oops I understand now you were taking the mean there! My bad, not sure why I thought that was a seperate fancy MATLAB thing.

[Matt J]

Instead of separate variables,

in_mp=[1,2,3],

in_mp = 1×3

1 2 3

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in_bof=[11,12,13],

in_bof = 1×3

11 12 13

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you should have

in.mp=[1,2,3];
in.bof=[11,12,13],

in = struct with fields:
     mp: [1 2 3]
    bof: [11 12 13]

As you can see from the ouput, this packages the mp and bof data into a single structure (struct) variable called 'in'. Since the fields mp, bof, etc... are now held under 'in', you can loop over them and/or operate on them as a group with commands like structfun.

[Umar]

Hi @Sophie,

Since you mentioned you are new to structs, here is a simple way to compute all your percentages and the combined mcusing the struct approach @Matt J described. This keeps everything in one place and avoids multiple separate variables:

% Store your data in a struct
in.mp    = [1 1 0 1 0];
in.mb    = [0 1 1 1 1];
in.cob   = [1 0 1 1 0];
in.mcup  = [1 0 0 1 1];
in.mclow = [0 1 1 0 1];
in.bof   = [1 0 1 0 0];

% Preallocate struct for percentages
fields = fieldnames(in);
Percentageoftime = struct();

% Compute mean (percentage) for each field
for k = 1:numel(fields)
  f = fields{k};
  Percentageoftime.(f) = mean(in.(f));
end

% Compute combined MC percentage
Percentageoftime.mc = Percentageoftime.mcup + Percentageoftime.mclow;

% Display results
disp(Percentageoftime)

Why this works

• in stores all your datasets under descriptive field names, so you don’t need many separate variables.
• mean(in.(f)) calculates the percentage of 1’s in each dataset, which is equivalent to your original sum/length.
• The loop handles all fields automatically, so it’s easy to add more datasets later.
• Combined mc is calculated after all individual percentages, keeping it simple.

Example output:

This should make it easier to understand and implement while keeping your code concise.