# Loop over an array

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Alessandro Ruda am 21 Feb. 2022
Bearbeitet: Jan am 22 Feb. 2022
Dear MatLab comunity,
I have a problem with a for loop.
I have two arrays of angles Theta1 and Theta2 (attached).
I have defined the following:
Theta1 = Theta1(:,2); %% which are the Theta1 angles
Theta2 = Theta2(:,2); %% // Theta2 angles
Theta1_cis = Theta1((Theta1 > -90) & (Theta1 < 90)); % Array of values when theta1 is in Cis
Theta1_trans = Theta1(Theta1 > 90 | Theta1 < -90); % Array of values when theta1 is in Trans
What I need now is to define an array such that when Theta1 is whitin the cis range then I collect the value in the variable Theta2_T1cis otherwise it goes in Theta2_T1trans, or when Theta1 is in the trans range then it goes in Theta2_T1trans.
I tried to put up a loop but I am very nabish so please help me on this:
i = 1;
for i = 1:[Theta1]
if Theta1((Theta1 > -90) & (Theta1 < 90))
Theta2_T1cis(i) = Theta2(i)
else Theta2_trans(i) = Theta2(i)
i= i+1;
end
end
this is not working of course. How can I solve it?
Hope the question is clear, otherwise I will reformulate.
Alessandro
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### Akzeptierte Antwort

Jan am 21 Feb. 2022
Bearbeitet: Jan am 21 Feb. 2022
There is no need for a loop:
T1_cis_index = (Theta1 > -90) & (Theta1 < 90);
T1_trans_index = (Theta1 > 90) | (Theta1 < -90);
Theta1_cis = Theta1(T1_cis_index);
Theta1_trans = Theta1(T1_trans_index);
Theta2_T1cis = Theta2(T1_cis_index);
Theta2_T1trans = Theta2(T1_trans_index);
By the way, this is no the way loops are working. A cleaner version:
% i = 1; Nope
for i = 1:numel(Theta1) % Not: [Theta1]
if (Theta1(i) > -90) & (Theta1(i) < 90)) % Use Theta1(i), not the complete vector
Theta2_T1cis(i) = Theta2(i)
else
Theta2_trans(i) = Theta2(i)
% Nope: i= i+1;
end
end
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Alessandro Ruda am 21 Feb. 2022
Bearbeitet: Alessandro Ruda am 21 Feb. 2022
Ok, it actually works. But I had to change it this way to obtain what I wanted specifically.
for i = 1:numel(Theta1)
if ((Theta1(i) > -90) & (Theta1(i) < 90))
Theta2_T1cis_raw(i) = Theta2(i);
else
Theta2_T1trans_raw(i) = Theta2(i);
end
end
tTheta2_T1cis = Theta2_T1cis_raw(Theta2_T1cis_raw~=0);
Theta2_T1cis = transpose(tTheta2_T1cis);
tTheta2_T1trans = Theta2_T1trans_raw(Theta2_T1trans_raw~=0);
Theta2_T1trans = transpose(tTheta2_T1trans);
I don't know if it can be made cleaner!
Thank you anyway!
Jan am 22 Feb. 2022
Bearbeitet: Jan am 22 Feb. 2022
The loop is not needed. A shorter, leaner and faster solution:
match = (Theta1 > -90) & (Theta1 < 90);
Theta2_T1cis = Theta2(match);
tTheta2_T1trans = Theta2(~match);

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