Problem with while loop, index is set back
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I try to compare two line vectors in a way that the following is supposed to happen:
As long as a "0" is detected in vector1, then the index in the result-vector u is also "0". As soon as a "1" is detected, the value of vector2 is to be written to "u" until another "1" is detected in vector1.
The following example should illustrate what I mean:
vector1 = [0 0 0 0 1 0 0 0 0 0 1 0 0 0 0];
vector2 = [0 0 1 1 1 1 1 1 0 1 1 1 1 0 0];
The result should be:
u = [0 0 0 0 1 1 1 1 0 1 1 0 0 0 0]
Instead I get:
u = [0 0 0 0 1 0 0 0 0 0 1 1 1 0 0]
My code:
u = zeros(1,size(vector1,2));
for i = 1:size(vector1,2)
if vector1(1,i) == 0
u(1,i) = 0;
else
u(1,i) = 1;
i = i+1;
while vector1(1,i) <1
u(1,i) = vector2(1,i);
i = i+1;
end
u(1,i) = 1;
end
end
I ran the debugger and the following happens: At i = 5 the first "1" is detected and the else statement with while loop starts. As soon as it enters the while loop, i is increased correctly. When the second "1" is detected in vector1, it exists the while loop correctly. u looks like this:
u = [0 0 0 0 1 1 1 1 0 1 1 0 0 0 0]
i = 11
But then, on the next turn, starting with the next "if" statement at the beginning, i is set back to i = 6 as if the while loop was never entered. Then the already existing spots are overwritten by "0" again. Probably something simple with overwriting i , but I have been trying to figure it out for the past 2 hrs and just couldn't solve it.
Thank you for your help!
采纳的回答
Roger Stafford
2014-8-24
It is not clear whether at the second '1' in vector1 of your example the '1' that is put into 'u' is copied immediately from vector1 or there is a delay by one position and it is still being copied from vector2. I am assuming the former of these. I also assume that copying from the two vectors continues to alternate between them as 1's alternately occur in vector1.
Try this (call vector1 and vector2, v1 and v2, resp.):
f = find(v1>0);
f1 = f(1:2:end);
f2 = f(2:2:end);
u = zeros(size(v1));
u(f1) = 1;
u(f2) = -1;
u = cumsum(u);
u = v1.*(u==0)+v2.*(u==1);
更多回答（1 个）
You can't overwrite i. for loops in matlab do not work like that. At each iteration of the for, i takes the next value in the vector [1 2 3 ... size(vector1, 2)].
If you do want to your computation with a for loop, I would just use a flag to tell me whether to copy or not the element at each iteration. You toggle the flag whenever you encounter a one in vector1:
u = zeros(size(vector1));
docopy = false;
for idx = 1 : numel(vector1)
if vector1(idx) == 1
u(idx) = vector2(idx); %always copy when 1
docopy = ~docopy; %toggle flag
else
u(idx) = docopy & vector2(idx); %will always be 0 if docopy is false
end
end
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