# Avoiding many if-Statetments in a for-loop

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Kilian Helfenbein on 11 Dec 2019
Edited: Adam Danz on 11 Dec 2019
Hello everyone :)
I would like to run a for-loop over a vector. What to do with each element in the vector depends on many if-else statements. I simplified it like this:
clear variables;
rng default;
V1 = rand(365,1);
V2 = rand(365,1);
V2 = V2 <= 0.5;
V3 = rand(365,1);
V3 = V3 <= 0.3;
Vresult = zeros(length(V1),1);
tstart = 1;
tend = length(V1);
for t = tstart:tend
if V2(t) == 1
if V3(t) == 1
Vresult(t) = do_stuff(V1(t));
else
Vresult(t) = do_different_stuff(V1(t));
end
else
if V3(t) == 1
Vresult(t) = do_even_different_stuff(V1(t));
else
Vresult(t) = do_even_more_different_stuff(V1(t))
end
end
end
function [var_out] = do_stuff(var_in)
var_out = var_in * 5;
end
function [var_out] = do_different_stuff(var_in)
var_out = var_in + 3;
end
function [var_out] = do_even_different_stuff(var_in)
var_out = var_in / 4;
end
function [var_out] = do_even_more_different_stuff(var_in)
var_out = var_in - 2;
end
With even more if-else conditions and more calculations per statement it gets really confusing and unreadable. And I feel like I'm writing the same code over and over again as only some parts of the code are different in each statement and other parts stay the same.
How can I make my code more efficient, easier to read and maintainable? Sorry if this should be common knowledge :D
Adam Danz on 11 Dec 2019
If those functions can be vectorized, the best approach is illustrated by the answer provided by "Adam". If you need to perform those functions on each value of V1 within a loop, the answer provided by myself ("Adam Danz") is a bit cleaner than nested conditional statements.

Adam Danz on 11 Dec 2019
I'm assuming the local functions provided are just demo functions. If those functions can be vectorized, it's very likely that you don't need a loop or any conditional statements at all.
Here's a method of performing a function on each element of vector V1 based on the values of V2(n) and V3(n) which are both logical vectors. It uses a switch-case instead of a series of conditional statements. The switch expression must be a scalar or char vector which is why I'm converting the logical values to char where 1 is true and 0 is false.
VAll = [V2,V3];
for t = tstart:tend
switch sprintf('%d %d',VAll(t,:))
case '1 1'
Vresult(t) = do_stuff(V1(t));
case '1 0'
Vresult(t) = do_different_stuff(V1(t));
case '0 1'
Vresult(t) = do_even_different_stuff(V1(t));
case '0 0'
Vresult(t) = do_even_more_different_stuff(V1(t));
otherwise
% This should never happen unless VAll is unexpected
error('Something is unexpected about the internal variable ''VAll''.')
end
end
##### 2 CommentsShowHide 1 older comment
Adam Danz on 11 Dec 2019
I like the idea of using numbers rather than char vectors (clever use of polyval!). VAll is an nx2 logical matrix so the switch would need to be
VAll = [V2, V3];
for t = tstart:tend
switch polyval(VAll(t,:),2)
case 0 % V2 = 0, V3 = 0
case 1 % V2 = 0, V3 = 1
case 2 % V2 = 1, V3 = 0
otherwise % V2 = 1, V3 = 1
end
end

Edited: Adam on 11 Dec 2019
Something like this would seem to do the job, off the top of my head, though I may be over-simplifying it...
case1 = V2 && V3;
case2 = V2 && ~V3;
case3 = ~V2 && V3;
case4 = ~V2 && ~V3;
Vresult( case1 ) = do_stuff( V1( case1 ) );
Vresult( case2 ) = do_different_stuff( V1( case2 ) );
Vresult( case3 ) = do_even_different_stuff( V1( case3 ) );
Vresult( case4 ) = do_even_more_different_stuff( V1( case4 ) );

R2019b

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