How to call a variable with user string input

Hi all,

I know this is a likely a simple problem, but am having lots of trouble...

I am trying to use an array of data (say 1x50) in a for loop from a user input that is different than the name of the array.

In other words, the user inputs something like 'example' and I need to use the data in the existing array that is named 'exampleD'

      exampleD = ones(1,50); % this is an existing array

      inp = input('Which dataset are you working with? ','s');
      % at this point user enters the string 'example'

Missing code here (some command that will concatenate user input and the letter 'D' to get 'exampleD' which is the name of the existing variable)

      for i = 1:50
          fprintf(fid,'%f',exampleD(i));
          fprintf(fid,',');
      end

Any help is greatly appreciated!

[Jorge Ignacio Cisneros Saldana]

Do you know how to do same approach without eval command for a parfor loop?.

eval(['dataset = ',variableName,';']);

[Walter Roberson]

If you were able to do an assignment by eval() inside the body of a parfor, there would be no way for matlab to know that the variable had to be returned to the client. If it were possible at all, then it would only be useful for assigning to local variables. And if you are going to be creating local variables you might as well use dynamic field names inside a struct instead of using eval()

Remember that you can assign a struct into a cell array, and then after the parfor merge the struct. Or output a cell of names and a cell of values and then cell2struct after the parfor

Answer 1

[Benjamin Avants]

Although it is often advised not to use this method, it would suit your purpose.

Once you have the user's input string and have created the variable name, you can use the eval function to access that variable.

eval(['dataset = ',variableName,';']);

the chosen dataset will now be stored in the variable 'dataset' and you can use it as per normal.

You could also store all the datasets as fields of a struct and use the variable name string to access the correct field of the struct.

[Roberto]

it's highly NOT recommended to use eval to assign variable names...

% Instead of this

eval('myVar = myfunc(2)');

% try this

myVar = eval(myfunc(2));

[Chris]

Thanks a ton Benjamin and Roberto. Between these last two comments I am able to write just a few lines of code to figure out my issue.

Answer 2

[Roberto]

exampleD = ones(1,50); % this is an existing array
inp = input('Which dataset are you working with? ');
for i = 1:numel(inp)
  % whatever
end

[Chris]

Roberto, Thanks for your answer, but this doesn't actually seem to help. My problem lies in the fact that my script needs to call a variable with an 'incomplete' user input. -Chris

Answer 3

[Roberto]

exampleD = ones(1,50); % this is an existing array
inp = input('Which dataset are you working with? ','s');
% at this point user enters the string 'example'
inp = eval([inp 'D']);
for i = 1:50
  fprintf(fid,'%f',inp);
  fprintf(fid,',');
end

[Chris]

Thanks Roberto