using vertcat to convert a number of variables in the workspace into a column vector

Hi,

I have a number of variables in my workspace that I believe are arrays, each contain just one single value, and I am trying to organise them into a single column vector.

However when i try to use the vertcat function I am faced with a problem. The variables in my workspace are called P1,P2,P3,P3,....,P1650 and when I use the function: vertcat(P1:P1650) it just produces a 1 x 0 empty double row vector. But when I type in individual variables e.g. vertcat(P1,P2,P3,P4,P5,P6,P7,etc) it concatenates them as I would like.

Does anyone know what I am doing wrong here?

many thanks!

[Stephen23]

"The variables in my workspace are called P1,P2,P3,P3,....,P1650"

How did they get there? Although there are hack-fixes using eval to resolve the bad idea of having lots of numbered variables, the best solution is to avoid this whole problem altogether, e.g. if you simply load into a structure.

"Does anyone know what I am doing wrong here?": acessing variable names dynamically will be slow, buggy, obfuscated code. You should read this:

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

Answer 1

[Star Strider]

You have a problem that you didn’t create, know as ‘dynamically named variables’. I don’t know from your description if they are arrays or single values. The eval function can put things back to rights and create your vertically-concatenated array:

For single values —

[P1,P2,P3,P4,P5] = deal(1,2,3,4,5);                     % Assign Variables

for k1 = 1:5
    C(k1,:) = eval(sprintf('P%d', k1));                 % Create Column Vector
end

For arrays of possibly different sizes —

for k1 = 1:5
    C{k1,:} = eval(sprintf('P%d', k1));                 % Vertically-Concatenated Cell Array
end