Simple rounding numbers in a matrix

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André Pacheco
André Pacheco 2012-12-21
Hello,
I have a matrix that consist in a bunch of numbers. Por exemple matrix(a)=
1.46101448605678 0.124416958027372
0.00918754579219433 -0.0655659591723838
0.549665183459168 0.218046503150596
What i want to do is make something that can round my numbers to 0, -1 and 1. If the number in the matrix is <-0,5 it should put -1 if it is bigger than 0.5 it should put 1. And the other numbers put into 0.
Thanks in advance.

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采纳的回答

Azzi Abdelmalek
Azzi Abdelmalek 2012-12-21
编辑：Azzi Abdelmalek 2012-12-21
A=2*rand(5)-1 % Example
A(A<-0.5)=-1;
A(A>0.5)=1;
A(-0.5<A & A<0.5)=0
  2 个评论
André Pacheco
André Pacheco 2012-12-21
It works, but it changes the structure of my matrix. Don't know why. My matrix is a 2x5 and after that it changes to a 1x10. Do you know why?
André Pacheco
André Pacheco 2012-12-21
Oh, i solved this initiating the new matrix with zeros.

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更多回答（3 个）

Roger Stafford
Roger Stafford 2012-12-21
编辑：Roger Stafford 2012-12-21
b = (a>.5)-(a<-.5);
Roger Stafford
Image Analyst
Image Analyst 2012-12-21
Andre, if you have the Image Processing Toolbox, you can quantize your array with the imquantize function in a single line of code:
m=[...
1.46101448605678 0.124416958027372
0.00918754579219433 -0.0655659591723838
0.549665183459168 0.218046503150596]
m_quantized = imquantize(m, [-0.5, 0.5])-2
In the command window:
m =
1.46101448605678 0.124416958027372
0.00918754579219433 -0.0655659591723838
0.549665183459168 0.218046503150596
m_quantized =
1 0
0 0
1 0
Shaun VanWeelden
Shaun VanWeelden 2012-12-22
编辑：Shaun VanWeelden 2012-12-22
Not to assume anything, but as a tutor for MATLAB, I have seen this question many, many times. If you are starting out in MATLAB, a good and easy approach is to use for loops and an if-else statement
[rows columns]=size(yourMatrix)
for i=1:rows
for j=1:columns
if yourMatrix(i,j)>.5
yourMatrix(i,j)=1
elseif yourMatrix(i,j)<-.5
yourMatrix(i,j)=-1
else %its between those two
yourMatrix(i,j)=0
end
end
end
I hope that helps you and anyone else, let me know if you have more questions :)
  1 个评论
Image Analyst
Image Analyst 2012-12-22
Do your students then tend to use this loop based approach even after they've been shown the vectorized approach? Or do they switch over immediately once they learn the vectorized approach after this? I've seen people use loops for matrices that are millions of elements, even though they've been using MATLAB for months or years, when they could have used a faster vectorized approach instead.

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