Matlab: Series of Variables in a Loop

Question

This is a solution from another stackoverflow participant who helped me out. Data is coming from a csv file:

    States Damage Blizzards

    Indiana 1      3
    Alabama 2      3
    Ohio    3      2
    Alabama 4      2


%// Parse CSV file
[States, Damage, Blizzards] = textread(csvfilename, '%s %d %d', ...
    'delimiter', ',', 'headerlines', 1);

%// Parse data and store in an array of structs
[U, ix, iu] = unique(States);        %// Find unique state names
S = struct('state', U);              %// Create a struct for each state
for k = 1:numel(U)
    idx = (iu == k);                 %// Indices of rows matching current state
    S(k).damage = Damage(idx);       %// Add damage information
    S(k).blizzards = Blizzards(idx); %// Add blizards information
end

In MATLAB, I need to create a series of assigned variables (A1,A2,A3) in a loop. So I have structure S with 3 fields: state, tornado, hurricane.

Now I have attempted this method to assign A1 =, A2 =, which I got an error because it will not work for structures:

   for n = 1:numel(S)
   eval(sprintf('A%d = [1:n]',S(n).states));
   end

Output goal is a series of assigned variables in the loop to the fields of the structure:

  A1 = 2 3
  A2 = 2 3
  A3 = 4 5

I'm not sure that this is the 'Matlab-way' of doing things, as explained here — Schorsch
– Schorsch, Commented May 9, 2013 at 19:53
@user1608954 Why do you need a bunch of variables with different names? Why not create another field in the structure for that, or at least use cell arrays? — Eitan T
– Eitan T, Commented May 9, 2013 at 20:06
Well, I'm generating a different variable name so I can plot the different variables. Schorsch, here is a structure: S = struct('Texas', 0, 'Kansas', 1, 'Maryland', 2) — Minimalist
– Minimalist, Commented May 9, 2013 at 20:16

Schorsch · Accepted Answer · 2013-05-10 14:43:10Z

1

I'm not 100% sure I understand your question.
But maybe you are looking for something like this:

for n = 1:numel(S)
   eval(sprintf('A%d = [S(n).damage S(n).blizzards]',n));
end

BTW using evalc instead of eval will suppress the command line output.

A little explanation, why

eval(sprintf('A%d = [1:n]',S(n).state));

does not work:

S(1).state

returns

ans = 
   Alabama

which is a string. However,

A%d

expects a number (see this for number formatting).
Additionally,

numel(S)

yields

ans = 
   3

Therefore,

eval(sprintf('A%d = [1:n]',n));

will simply return the following output:

A1 =

 1

A2 =

 1     2

A3 =

 1     2     3

Hence, you want n as a counter for the variable name, but compose the vector of the entries in the other struct-fields (damage and blizzards), again, using n as a counter.

edited May 10, 2013 at 14:43

answered May 9, 2013 at 20:59

Schorsch

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1 Comment

Minimalist Over a year ago

THAT'S IT. Thanks, Schorsch. I had been working with something similar, but just couldn't complete it. Thanks a lot.

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