How to separate all negative and all positive values of a vector?

Hello, I baffled by one task in Matlab, namely I need to create two vectors that contains all positive and all negative values of an initial vector. I would like to get a general answer to my question. Here is my script (unfinished): for i=1:numel(x) if x(i) > 0 & x(i)==0 P(i)=????????(all positives) end end disp('The postive vector is:')

Sergey

Answer 1

[Stephen23]

You don't need a loop, because logical indexing is much simpler and faster:

>> X = [1,2,-3,-4,5,-6,7,-8,9];
>> idx = X<0; % create logical index
>> neg = X(idx)
neg =
  -3  -4  -6  -8

>> pos = X(~idx)
pos =
   1   2   5   7   9

[Saranya A]

Thanks Stephen for the logical indexing idea!

What if I want the dimension of neg and pos to be the same as X?

Eg: I want neg=[0,0,-3,-4,0,-6,0,-8,0] and pos=[1,2,0,0,5,0,7,0,9]

[Walter Roberson]

pos = 0*X;
pos(~idx) = X(~idx);

or more simply

pos = max(0, X);

[Rhian Enders]

Can you do this with two vectors?

[Walter Roberson]

@Rhian Enders

Do we understand correctly that there should be 11 different outputs?

1. element in first vector and second vector are both positive
2. element in first vector is positive, element in second vector is zero
3. element in first vector is positive, element in second vector is negative
4. element in first vector is zero, element in second vector is positive
5. element in first vector is zero, element in second vector is zero
6. element in first vector is zero, element in second vector is negative
7. element in first vector is negative, element in second vector is positive
8. element in first vector is negative, element in second vector is zero
9. element in first vector is negative, element in second vector is negative
10. element exists in first vector but you have run out of elements in the second vector
11. element exists in second vector but you have run out of elements in the first vector

Or should the cases where you have run out of elements in one of the vectors each be split into the negative / zero /positive, leading to a total of 15 different cases?

[Brice Arthur Azangue]

Stephen23 thanks for this short line code.

Answer 2

[RAM MANOHAR]

I have used for , if --else loops but i have got positive and 0 in place of negative.

[Narendra Kintali]

Hi Ram,

I even got zeros in the place of negative numbers.

How did you fix your code.

[Walter Roberson]

Stephen23's code is fine, https://www.mathworks.com/matlabcentral/answers/244614-how-to-separate-all-negative-and-all-positive-values-of-a-vector#answer_193412