Simple rounding numbers in a matrix

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André Pacheco
André Pacheco el 21 de Dic. de 2012
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.

Respuesta aceptada

Azzi Abdelmalek
Azzi Abdelmalek el 21 de Dic. de 2012
Editada: Azzi Abdelmalek el 21 de Dic. de 2012
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 comentarios
André Pacheco
André Pacheco el 21 de Dic. de 2012
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 el 21 de Dic. de 2012
Oh, i solved this initiating the new matrix with zeros.

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Más respuestas (3)

Roger Stafford
Roger Stafford el 21 de Dic. de 2012
Editada: Roger Stafford el 21 de Dic. de 2012
b = (a>.5)-(a<-.5);
Roger Stafford

Image Analyst
Image Analyst el 21 de Dic. de 2012
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 el 22 de Dic. de 2012
Editada: Shaun VanWeelden el 22 de Dic. de 2012
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 comentario
Image Analyst
Image Analyst el 22 de Dic. de 2012
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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