How can I use different array names in a loop?

Hello,

Suppose I have 4 arrays as,

a_1_b; 

a_2_b; 

a_3_b; 

a_4_b

all the arrays are of same size. I want to add something in the first column of each of the arrays, but I am not sure how to do this. as example:

for i=1:4

a_i_b(:,1)=a_i_b(:,1)+7

end

this is not the right way. Can anyone please show me the correct way?

Thanks!

Answer 1

[Azzi Abdelmalek]

for i=1:4
 evalin('base',sprintf('a_%d_b(:,1)=a_%d_b(:,1)+7',i,i))
end

%or

for i=1:4
  data=7
  evalin('base',[sprintf('a_%d_b(:,1)=a_%d_b(:,1)+',i,i) num2str(data)])
end

[Jan]

Avoid EVAL and EVALIN in general. Both increase the komplexity and reduce the efficiency, and there are always cleaner and faster methods.

Answer 2

[Jan]

See http://www.mathworks.com/matlabcentral/answers/57445-faq-how-can-i-create-variables-a1-a2-a10-in-a-loop: It is strongly recommended not to hide indices in the names of variables, but touse indices instead.

ab    = cell(1, 4);
ab{1} = rand(2,3);
ab{2} = rand(2,3);
ab{3} = rand(2,3);
ab{4} = rand(2,3);
for k = 1:4
   ab{k}(:,1) = ab{k}(:,1) + 7
end

[Nazmul]

thanks a lot, Simon... That FAQ was also helpful.

Answer 3

[Andrei Bobrov]

n = sprintf('a_%d_b,',1:4);
a_b = eval(['{',n(1:end-1),'}']);
a_b = cellfun(@(x)[x(:,1) + 7,x(:,2:end)],a_b,'un',0);

Answer 4

[Nazmul]

Thanks a lot. All the 3 solutions were helpful.