Creating a logic vector out of 2D matrix

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Lama Hamadeh
Lama Hamadeh 2022-4-27
评论： Jon 2022-4-27
Hi,
How can I create a logic vector v out of a matrix M in a way that each row of v equals to 1 when the second element of Mper row equals to 0, as illustrated below:
My attempt in coding this is as following:
%M matrix
M = [1 2;
2 0;
3 1;
4 0;
5 3;
6 0;
7 2;
8 4;
9 0;
10 1];
%initialise v vector
v = [];
%create v vector
for i =1:size(M,1)
if M(i,i) == M(i,0)
v(i) = 1;
else
v(i) = 0;
end
end
An error message of "Index in position 2 is invalid. Array indices must be positive integers or logical values." apears.
Any help would be appreicted.
Thanks.

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回答（3 个）

Dyuman Joshi
Dyuman Joshi 2022-4-27
Ran in:
Indexing in MATLAB starts with 1 and not 0.
M = [1 2;
2 0;
3 1;
4 0;
5 3;
6 0;
7 2;
8 4;
9 0;
10 1];
%initialise v vector
v = [];
%create v vector
for i =1:size(M,1)
if M(i,2) == 0 %Comparing 2nd element of ith row to 0 as you mentioned
v(i,1) = 1;
else
v(i,1) = 0;
end
end
v
v = 10×1
0 1 0 1 0 1 0 0 1 0
Fangjun Jiang
Fangjun Jiang 2022-4-27
编辑：Fangjun Jiang 2022-4-27
M(i,i) == M(i,0)
should be
M(i,2) == 0
When you have this type of error on a very simple script, put a break point and run the script line by line. You will be able to debug the problem by yourself.
Jon
Jon 2022-4-27
%M matrix
M = [1 2;
2 0;
3 1;
4 0;
5 3;
6 0;
7 2;
8 4;
9 0;
10 1];
% logic vector
v = ~M(:,2)
  1 个评论
Jon
Jon 2022-4-27
The above uses the fact that MATLAB treats double values which are zero as if they were logical false. You could also do what you want, maybe more clearly using
v = M(:,2)==0

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