Logical Indexing with zero and one. Getting only the change from 0 to 1 and from 1 to 0.

2013 6 12
2 个回答
3 次查看（30 天）

0 个投票

Is there any way to from matrix A to matrix B without using find?
A= B=
0 0
0 0
0 0
0 0
0 0
0 0
1 1
1 0
1 0
1 0
1 1
0 0
0 0
0 0
0 0
0 0
Thank you.

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回答（2 个）

Andrei Bobrov
Andrei Bobrov 2013-6-12
编辑：Andrei Bobrov 2013-6-12

0 个投票

B = [0;diff(A)==1] + flipud([0;diff(A(end:-1:1))==1]);
B = [false;diff(A)==1] | flipud([false;diff(A(end:-1:1))==1]); % logical
Giorgos Papakonstantinou
编辑：Giorgos Papakonstantinou 2013-6-12

0 个投票

The correct should be like this. After playing around a bit I found this.
%%Example
a=0:0.01:0.12;
b=0.13:-0.01:0.03;
c=0.04:0.01:0.13;
d=0.12:-0.01:0.02;
mat=vertcat(a',b',c',d');
mat(:,2)=mat(:,1)>0.04;
mat(:,3)=[0; diff(mat(:,2))];
mat(:,4)=mat(:,3)==1;
mat(:,5)=[diff(mat(:,2)); 0];
mat(:,6)=mat(:,5)==-1;
mat(:,7)=mat(:,6)|mat(:,4);
So in this way you can index the boundaries. I would like also other people's opinion. If such a way is efficient or not. is it better to index them with find? thank you

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Image Analyst
Image Analyst 2013-6-12
I have no idea what this is about. This code has no relation to your original question whatsoever. But if it does what you want, go for it. No one cares about efficiency when you're only dealing with 315 elements. What would you save - a nanosecond? Now if you had 315 million elements, then it would be a concern.

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