CODEWITHSUNDEEP
matlab
MikeH
MikeH

Reputation: 47

Storing result in a matrix

I have a problem with storing results in a matrix. a is my time series with a certain rate. Now I would like to have that rate quarterly, so I did the following:

a = [1 4.2; 2 3.9; 3 3.7; 4 3.9; 5 4.1; 6 4.3; 7 4.2; 8 4.1; 9 4.4; 10 4.5; 11 5.1; 12 5.2;13 5.8]

for K = 1:3:10;
    result(K, 1) = a(K+3, 2)-a(K, 2)
end

Unfortunately, the result vector is now a 10x1 vector, but actually I would like it to be a 4x1 vector only with the 4 quarterly values. For the given example my desired output would be [-0.3 0.3 0.3 1.3].

Anyone an idea how to do so? Any help appreciated!

Upvotes: 1

Views: 46

Answers (1)

HansHirse
HansHirse

Reputation: 18905

As explained in Patrick Happel's comment, in your example, K have will values from [1 4 7 10]. By accessing result(K, 1) for K = 10, your result array "automatically" will have a size of 10x1.

To prevent that, you can "precalculate" the indices from K and access the corresponding elements in a directly without using any loop.

Here are the codes next to each other:

% Input
a = [1 4.2; 2 3.9; 3 3.7; 4 3.9; 5 4.1; 6 4.3; 7 4.2; 8 4.1; 9 4.4; 10 4.5; 11 5.1; 12 5.2;13 5.8]

% Using loop
for K = 1:3:10;
    result(K, 1) = a(K+3, 2)-a(K, 2);
end
result

% Using precalculated indices
K = 1:3:10;
result = a(K+3, 2)-a(K, 2)

And, the outputs:

a =
    1.0000    4.2000
    2.0000    3.9000
    3.0000    3.7000
    4.0000    3.9000
    5.0000    4.1000
    6.0000    4.3000
    7.0000    4.2000
    8.0000    4.1000
    9.0000    4.4000
   10.0000    4.5000
   11.0000    5.1000
   12.0000    5.2000
   13.0000    5.8000

result =
  -0.30000
   0.00000
   0.00000
   0.30000
   0.00000
   0.00000
   0.30000
   0.00000
   0.00000
   1.30000

result =
  -0.30000
   0.30000
   0.30000
   1.30000

Hope that helps!

Upvotes: 3

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