MATLAB: How to change string name

string name

Hey!

I have a function e.g. y=a*x.

How can I change later string name of y to y306 or sth like that?

Best Answer

The solution is to simply use indexing. For example, you could put all of your imported data into one cell array. You did not give much information in your question (e.g. the file format, what function you are using to import the data, the data class, whether you generate the name with sprintf or use dir to obtain the names of existing files, etc), so I will show an example that imports data from .mat files using load:

S = dir('*.mat');
N = numel(S);
C = cell(1,N); % preallocate.

for k = 1:N 
    C{k} = load(S(k).name);
end
A = [C{:}] % optional, create non-scalar structure.

Then all of the imported data will be available in the cell array C or (even better) the non-scalar structure A:

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

If the loaded .mat files only contain one (or a few) variables that you need, you can easily access them inside the loop and put that data into on (or a few) array, e.g.:

S = dir('*.mat');
N = numel(S);
C = cell(1,N); % preallocate.
for k = 1:N 
    T = load(S(k).name);
    C{k} = T.y;
end

Feel free to adapt the class and size to suit your data: depending on your data you could import into a numeric/char/string array, with columns/rows to suit number of variables, etc..

You should read this too:

https://www.mathworks.com/help/matlab/import_export/process-a-sequence-of-files.html

Related Solutions

MATLAB: Loading multiple *mat files

For a basic explanation see the MATLAB documentation:

https://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html

If all of the .mat files contain the same variables then try something like this:

files = dir('*.mat');
out = load(files(1).name);
for k = 2:numel(files)
    out(k) = load(files(k).name);
end

Your data is available in the non-scalar structure out, e.g.:

[out.F]

MATLAB: Extract *.mat-Variables with same names from different directories

"A simple 'load' command will give me a strut, which I can't do much with."

"Ideally, I'd like a workspace containing all 96 variables structurally named, like 'J_333_01_a'. From there, I should be able to process them further (plotting etc)"

Nope, you have that exactly the wrong way around. Loading data into lots of numbered (or otherwise uniquely named) variables would be the worst way of doing this. Loading into a structure and then either

storing the structure (could be non-scalar, if the fields are the same), or
extracting and storing the data within the structure

would be the fastest and most robust ways to do this. Read this to know why:

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

http://www.mathworks.com/matlabcentral/answers/196952-how-to-create-new-variables-in-batches-with-strcat

The best solution is to take a deep breath, and learn to love structures. Really, you can do more with structures than you can by loading that data into independent variables. All of those things that you imagine doing: looping over your data, concatenating the data into numeric array is trivial when you have load-ed into a structure. Load them into separate variables and you will be writing the slowest, buggiest, and most obfuscated code in town.

Incidentally when you try to access variables dynamically all of MATLAB Editor's helpful tools (variable highlighting, code checking, error checking, f1 help, syntax help, etc, etc) do not work: why beginners prefer to use dynamic variable access which disables all of the MATLAB tools that help them to write good code is a mystery.

Have a look at this simple example (which I just copied from this question):

First we create some fake data:

>> A = 1:3;
>> save('file1.mat','A');
>> A = 4:6;
>> save('file2.mat','A');
>> A = 7:9;
>> save('file3.mat','A');

Now we get a list of those mat files, and read them in a loop:

S = dir('*.mat');
for k = 1:numel(S)
    tmp = load(S(k).name);
    S(k).A = tmp.A;
end

Now all the data is in structure S, and it is easy to access:

>> vertcat(S.A)
ans =
     1     2     3
     4     5     6
     7     8     9
>> S(3).A
ans =
     7     8     9

You should definitely read this: http://www.mathworks.com/help/matlab/matlab_prog/access-multiple-elements-of-a-nonscalar-struct-array.html, and practice with the examples.

Of course you don't have to store the data in a structure, it is also trivial to store them in an array:

>> S = dir('*.mat');
>> M = NaN(numel(S),3);
>> for k = 1:numel(S), tmp = load(S(k).name); M(k,:) = tmp.A; end
>> M
M =
     1     2     3
     4     5     6
     7     8     9

Best Answer

Related Solutions

MATLAB: Loading multiple *mat files

MATLAB: Extract *.mat-Variables with same names from different directories

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