How to remove sets of values from a column vector using two column vectors with the starting and stopping indeces for removal by row

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Shawn
Shawn 2016-8-2
评论： Shawn 2016-8-2
Let's say that I have a column vector, x
x = (1:10)'
and two column vectors with the starting and stopping indeces, x_start and x_stop
x_start = [2; 7]
x_stop = [5; 8]
such that I want to remove the values 2->5 and 7->8.
I could use a simple for loop, such as the following:
for i = length(x_start):1
a = x_start(i)
b = x_stop(i)
x(a:b) = []
end
However, I would look to avoid using a for loop as my vector lengths are on the order of 10^5. Is there a more computationally efficient manner to build the indeces that I want to remove from my starting and stopping vectors?

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采纳的回答

Fangjun Jiang
Fangjun Jiang 2016-8-2
This method uses string. Not sure if it is more efficient.
num=[x_start,x_stop]';
str=sprintf('%d:%d,',num(:));
x(str2num(str))=[];
  2 个评论
Shawn
Shawn 2016-8-2
This is an interesting answer, but it does not seem to be working for length(x_start)~=2.
If I use x_start and x_stop with length 3 as:
x_start = [1,4,9]
x_stop = [2,7,10]
Then I return x = [5,6], but it should return x = [3,8] if I am removing 1->2, 4->7, and 9->10.
In this case, str = '1:4,9:2,7:10' rather than '1:2,4:7,7:10'. It does work on the length 2 case, but that was just pseudo-code to explain the problem. The actual vectors are much larger. Can this approach be expanded to account for that?

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