Concatenate variables with similar names

Dear all

I need to concatenate several variables with similar name.

For example: T=cat(3,SPL_A,SPL_B,SPL_C,SPL_D,SPL_E).

This procedure is easy when you have just a few variables, as I show you in the previous line, however in my case I have hundreds of variables which makes almost impossible to do it by hand.

The variables have all the same starting name which I guess could help in the process, but Im not realizing how to do it.

Thanks in advance

[SALAH ALRABEEI]

what is their pattern !! just SPL_ {A,B,C ,....}!! or there are numbers!

[Ricardo Duarte]

Yes, there are also numbers. The numbers are the only thing that change between different variables.

This is a typical name:

SPL_db_500Hz_position_1

and the number 500 and 1 change depending on the variable.

Thank you

[KSSV]

What is the necessity to concatenat??

[Ricardo Duarte]

I need to concatenate them for statistic purposes and because instead of having just:

T=cat(3,SPL_db_500Hz_position_1,SPL_db_500Hz_position_2,SPL_db_500Hz_position_3,SPL_db_500Hz_position_4,SPL_db_500Hz_position_5) i have hundreads of variables and it is impossible to do it by hand.

Thanks

[KSSV]

What is each variable? Is it a matrix?

[Ricardo Duarte]

yes

[Matt J]

@Ricardo Duarte How did you introduce so many variables into your workspace without typing them by hand?

[Ricardo Duarte]

Using a loop.

[KSSV]

So you are creating the variables. You could concatenate them while generating those variables in a loop.

Answer 1

[Stephen23]

"Using a loop."

Then that is where you should fix the bad code design.

Meta-data is data, so store it in arrays, not in variable names.

Forcing meta-data (e.g. positions, frequencies) into variable names is one way that beginners force themselves into writing slow, inefficient, complex code that is liable to bugs and yet difficult to debug:

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

"this procedure is easy when you have just a few variables"

It is also very easy when you have an arbitrary number of arrays. The simple and efficient solution is to keep your data in just a cell array, then you can use comma-separated lists to concatenate those arrays:

https://www.mathworks.com/help/matlab/matlab_prog/comma-separated-lists.html

https://www.mathworks.com/matlabcentral/answers/320713-how-to-operate-on-comma-separated-lists

For example:

N = number of arrays.
C = cell(1,N); % preallocate!
for k = 1:N
    ... your code
    C{k} = whatever output array you want
end
M = cat(3,C{:}); % so simple.

[Ricardo Duarte]

Thank you, but this will only concatenate the names of the variables and I want to concatenate the content of each variable.

[Ricardo Duarte]

It works, thank you

Answer 2

[SALAH ALRABEEI]

@Ricardo Duarte Here is a trick, you will save all your workplace into one variable b; then loop over all of them to take whose variables who have the same size ( which are those you want to concatenate ). Assuming your variables that you need to concatenate are of size 20 x 30. However, if a any variable the same size as 20 x 30 will be concatenated

b = whos;
ConMat = [];
for i = 1:length(b)
if sum(b(i).size) == sum([20,30])
ConMat=[ConMat;eval(b(i).name)];
end
end

[KSSV]

I am waitting for @Stephen Cobeldick answer. :)

[Ricardo Duarte]

Thank you, but in fact I need to use cat(3,variable1, variable2,etc) and I think that is diffent than using ConMat=[variable1, variable2, etc];

[SALAH ALRABEEI]

It would be great if there were a function that does so easily

[SALAH ALRABEEI]

@Ricardo Duarte, come on; this is just a trivial example, play with idea to get what you want.

[SALAH ALRABEEI]

Thank you @Stephen Cobeldick, I have just check you invaluable complete Tech report in the importance of properly naming the varaibles. I didn't expect that until I read part of it.

Regarding to my comment, I was expecting a faster way to fix the issue of @Ricardo Duarte ( where there are several variables. Thank you though.

[Stephen23]

"It would be great if there were a function that does so easily"

The comma-separated list syntax efficiently concatenates arbitrary numbers of arrays together.