# trying to use logical matrix to get remove some elements from matrix instead of getting a same matrix im getting a column matrix

6 views (last 30 days)
a=[1,2,3;12,21,2;2,1,2]
b=(a>1)
c=a(b)
im getting result
b =
0 1 1
1 1 1
1 0 1
c =
12
2
2
21
3
2
2
>> i want c matrix to be 3*3 matrix but im getting it as column matrix

Image Analyst on 25 Jun 2020
Try this:
a=[1,2,3;12,21,2;2,1,2]
c = a .* double(a > 1)

the cyclist on 25 Jun 2020
Edited: the cyclist on 25 Jun 2020
Assuming you want zeros in the other locations:
a=[1,2,3;12,21,2;2,1,2]
b=(a>1)
c = zeros(size(a));
c(b)=a(b)
c =
0 2 3
12 21 2
2 0 2

AJAY CHANDRA DORAGARI on 25 Jun 2020
what is exactly happening if we havent included the line
c=zeros(size(a))
why is it giving a result which i had mentioned above
the cyclist on 25 Jun 2020
I would think about it this way. The statement
a(a>1)
translates to "Give me the values of a for which a is greater than 1."
There are 7 such elements. MATLAB cannot "know" that you want those 7 elements arranged as they were before, and more critically, it cannot know that you want the "missing" two elements to be zero. It may be obvious to you that that is what is desired, but MATLAB cannot know that. Instead, maybe you (or someone else) actually wanted
c =
NaN 2 3
12 21 2
2 NaN 2
So, MATLAB is coded to return just the 7 elements requested, without making an assumption.
If, instead, you wanted a "mask" on your array that retains the shape, then you can instead code it the way I did, or Image Analyst did.
AJAY CHANDRA DORAGARI on 25 Jun 2020
thank you for explaining it clearly
thanks alot !!
the cyclist