For loop error: unable to perform assignment because left and right sides have a different number of elements

I am struggling to create a forloop which reduces the following task into a few lines of code:

             resp1 = squeeze(resp(:,1,:));
             resp2 = squeeze(resp(:,2,:));
             resp3 = squeeze(resp(:,3,:));
             resp4 = squeeze(resp(:,4,:));
             resp5 = squeeze(resp(:,5,:));
             resp6 = squeeze(resp(:,6,:));
             resp7 = squeeze(resp(:,7,:));
             
             imp_level(iter_rep-num_draw_discard,:,:) = resp1;
             imp_slope(iter_rep-num_draw_discard,:,:) = resp2;
             imp_curv(iter_rep-num_draw_discard,:,:) = resp3;
             imp_unrate(iter_rep-num_draw_discard,:,:) = resp4;
             imp_pce_ch(iter_rep-num_draw_discard,:,:) = resp5;
             imp_tcu_ch(iter_rep-num_draw_discard,:,:) = resp6;
             imp_effr(iter_rep-num_draw_discard,:,:) = resp7;
                    

I've tried the following but got an error

variables = {'level', 'slope', 'curv', 'unrate', 'pce_ch','tcu_ch', 'effr' };
            

range = linspace(1,size(variables,2),7);
  
% betas_exog is a (324 x 7) dimension matrix
for i = 1:size(betas_exog, 2)
    
    resp_range(i) = squeeze(resp(:,i,:));
    imp_variables{i}(iter_rep-num_draw_discard,:,:) = resp(i)
                
end          

I would appreciate your help in fixing the error and creating a workable for loop.

[Cris LaPierre]

What error message did you get? Please copy/paste the entire message (all the red text) here.

[matlabuser]

error: unable to perform assignment because left and right sides have a different number of elements

[James Tursa]

The general procedure for debugging this type of error is to type the following at the MATLAB command prompt:

dbstop if error

then run your code. When the error occurs, the code will pause with all variables intact. Examine all of the variables and expressions on the line that is generating the error to see what is causing the problem. Then backtrack in your code to figure out why the sizes are not what you expected.

[Stephen Cobeldick]

This won't work, it will not generate variable names like "imp_level" as your example shows:

variables = {'level', 'slope', 'curv', 'unrate', 'pce_ch','tcu_ch', 'effr' };
..
imp_variables{i}..

In any case, that approach is entirely wrong, unless you want to force yourself into writing slow, complex, inefficient, obfuscated code which is buggy and difficult to debug:

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

Instead of trying to access variable names dynamically, the much more efficient approach would be to use structure fields or a table. Or perhaps best of all: just leave the data and meta-data unchanged and access them using indexing. Or if you have a fixed, small number of such allocations, just write them out explicitly.

[J. Alex Lee]

Are you just trying to re-order the dimensions? Or would doing that first let you index more easily for whatever you are trying to do?

[matlabuser]

i was trying to just create a set of variables as defined above. To clarify, num_draw_discard is a scaler = 3000, iter_rep = 15,000.

Answer 1

[Gaurav Garg]

Hi,

You can plan to use either Structure array, or a Cell array. You could have also constructed variable name from string, however, the potential risks for it have already been pointed out, about which you can also look here.

The error which you are getting is usually caused when the dimensions of the assigner and the assignee variables are not the same/equal.

As the last option, you can look at Map Containers. They are the objects with keys that index to values, and at the same time, the keys need not be integers

[matlabuser]

thanks. that was helpful.