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

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AJAY CHANDRA DORAGARI
编辑： AJAY CHANDRA DORAGARI 2020-6-25
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

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采纳的回答

Image Analyst
Image Analyst 2020-6-25
Try this:
a=[1,2,3;12,21,2;2,1,2]
c = a .* double(a > 1)

更多回答（1 个）

the cyclist
the cyclist 2020-6-25
编辑：the cyclist 2020-6-25
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
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the cyclist
the cyclist 2020-6-25
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.

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