For loop running over different variables

Question

Good day,

I would like to do the following in Matlab:

var1 = 10;
var2 = 15;
var3 = 20;

j = 1;

for i = [var1,var2,var3]
    a(j) = i + 10;
    j = j + 1;
end
clear j;

With result:

a(1) = var1 + 10 = 20
a(2) = var1 + 10 = 25 
a(3) = var1 + 10 = 30

Any ideas?

what's wrong with `a = [var1, var2, var3] + 10`? It accomplishes the same. — Alexey, May 31 '13 at 19:24
Because my real situation is much more complex than this example. — Pietair, May 31 '13 at 19:25
I can't answer the question without knowing the real situation. What is your question? — Alexey, May 31 '13 at 19:26
I simply want a variables name within a loop to change every time the loop runs. — Pietair, May 31 '13 at 19:29
it is still not clear, can you provide a better illustrative example? — Alexey, May 31 '13 at 19:38

score 2 · Accepted Answer · answered May 31 '13 at 20:27

Engaging heavy use of crystal ball. It appears that you'd like to dynamically generate the names var1, var2, etc. Don't. There is just about never an advantage to naming variables this way. Use cell arrays instead:

var{1} = 10;
var{2} = 15;
var{3} = 20;

so that you can just use:

for i = 1:length(var)
    a(j) = var{i} + 10;
...

Note the curly brace.

If your variables are all the same size, it's even better to use array slices. var(:, i) or var(:,:,:,i), for example

score 0 · Answer 2 · edited May 23 '17 at 11:43

0

There was a similar question with a successful answer: foreach loop with strings in Matlab

maybe use the cell array syntax with {}:

for i = {var1,var2,var3}
a(j) = i + 10;
j = j + 1;
end

edited May 23 '17 at 11:43

Community

1
1

answered May 31 '13 at 19:29

FloHin

41
1
7

score 0 · Answer 3 · answered May 31 '13 at 21:01

Both @FloHin and @Peter have mentioned using cells, which is a great method to help you when you have a limited number of non-scalar variables. In case you are dealing with unknown number of such variables that follow a certain format, you can use eval function to get the value of the current variable on-demand:

var1 = 10;
var2 = 15;
var3 = 20;
var4 = 30;
# ...
# more variables following the varN = x pattern

all_variables = who('var*');
num = numel(all_variables);
a = zeros(num, 1);
for i = 1:num
    a(i) = eval(all_variables{i}) + 10;
end

For loop running over different variables

3 Answers3