how to refer variable from string name

Hello,

I have an array of string names for variables I need to use, and variables with such names in workspace. How should I refer? for example I need to find mean for variables with names 'm1_n' 'm3_n' specified in array A. The names will be different all the time -- I cant just write mean(m1_n) I need to do it through A and indexing, but in A names are strings.

[KSSV]

How you created that data? How the data is?

[Yelena Bibineyshvili]

the variables are different size number arrays

they are created in another programm

[Stephen23]

"they are created in another programm"

Sure, but so far you have not explained the most important piece of information: how did those variables get into your MATLAB worskpace? Did you write them out by hand? Or did some script create them? Or are they loaded from a file?

If you loaded them from a .mat file then the best solution is to load into an output variable (a scalar structure), which you should always be doing anyway, and then simply access the fields of that structure.

[Yelena Bibineyshvili]

yes they are created by other script

[Stephen23]

"yes they are created by other script"

The best** solution is to fix that other script so that it does not store meta-data (e.g. indices) in variable names.

** best in the sense more efficient (run-time, programming time, debugging time, maintenance time), easier to understand (simpler code, no obfuscation, clear where data comes from), easier to debug (variable highlighting, static code checking, mlint checking), etc.

Answer 1

[Jeff Miller]

This is pretty clumsy, but I think something like this will do what you want:

varnames = {'m1_n', 'm3_n'};  % names of the variables you want to process
save('temp.mat');  % save all workspace variables into a temporary mat file
g = load('temp.mat');  % load all variables into a "global" structure
x = mean(g.(varnames{1}));  % get the mean of the first named variable
y = max(g.(varnames{2}));   % get the mean of the second named variable

The keys are that (1) the load command makes a structure g with fields corresponding to the names of the original workspace vars, and (2) the syntax g.(s) picks out the field named by the string s.

Don't forget to delete temp.mat.

[Yelena Bibineyshvili]

thank you, this works

Answer 2

[Steven Lord]

Can you do this? Yes.

Should you do this? The general consensus is no.

Rather than defining variables with numbered names, consider putting them in an array.

x1 = 1:5;
x2 = x1 + 5;
x3 = x1 + 10;
% or
xmat = [x1; x2; x3];

To iterate through x1, x2, and x3 I'd need to use the discouraged approach. To iterate through the rows of xmat is easy.

for k = 1:size(xmat, 1) % or 1:height(xmat)
    y = xmat(k, :)
    % Do something with y
end

y = 1×5

1 2 3 4 5

y = 1×5

6 7 8 9 10

y = 1×5

11 12 13 14 15

[Yelena Bibineyshvili]

my variables are different size, I am getting them as a result of other programm

[Yelena Bibineyshvili]

and names are also generated by another person

[Steven Lord]

x = cell(1, 3);
for k = 1:3
    x{k} = magic(k+2);
end
for k = 1:3
    fprintf("Element %d of x is of size %s.\n", k, mat2str(size(x{k})))
end

Element 1 of x is of size [3 3].
Element 2 of x is of size [4 4].
Element 3 of x is of size [5 5].

[Yelena Bibineyshvili]

I already have variables and I want to avoid making another array from variables, here you write x=magic or random, but in my program I first will need to make that array from my varibles which have different names for each subject and different days. I need to know how to use variable with name specified in string.