How can I sorting the values in the jumping columns?

I have a matrices 25x600 and some columns contains positive and negative values. I want to the output like this [+ + - -] (four values 2 positive and 2 negative). I am guaranteed to always have two positive values immediately before the transition and two negative values immediately after. my attempting was as follow :

clc;
clear all;
close all;
data=[-0.0059972;-0.004994;-0.0029881;2.0868e-05;0.0030299;0.013059;0.033115;0.063196;0.093273;0.1935;0.39385;0.69423;0.99448;1.9950;3.99550;6.99550;9.9957;19.9961;39.99620;69.9960;99.99530;199.99810;399.99140;699.98860;1000.03130]
for r=1:600
    lam=data(:,r);
      N_lam = length(lam);
      for j=1:N_lam
          kk=0;
          r1=0;
          if(sign(lam(j))==1)
              kk=kk+1;
              lampos(kk)=lam(j);
              if (length(lampos(kk))>2 &length(lamneg(r1))>2)
               break
              end
          else
              r1=r1+1;
              lamneg(r1)=lam(j);
          end
      end
      cc{r}=[lampos lamneg];
end

Any help would be greatly appreciated. I will be grateful to you

[Guillaume]

What does pick four values mean, what do you want to return? Rather than posting code that's not valid (matlab does not have goto), post an example of input and wanted output.

In addition, are you guaranteed to always have two positive values immediately before the transition and two negative values immediately after?

[Ahmed]

Sorry but I run the code and I got one value positive and one negative but not as I want. Yes, I am guaranteed to always have two positive values immediately before the transition and two negative values immediately after

[Image Analyst]

First of all, you can't have a matrix like [+ + - -] - the best you can do is [1,1,-1,-1]. Or you could have any other values that have those signs I guess. But if that's it, then where, from an arbitrary matrix of a bunch of values, get those four values? You said "I want to the output like this [+ + - -] (four values 2 positive and 2 negative)." so which of the 15,000 elements would you extract to stick into the 4 element output array? Would I just pull 4 at random? I can't figure out what your for loop is doing - perhaps you can explain it in words. And it looks like it's looping over all elements so you will probably get more than 4 output values.

Answer 1

[Guillaume]

You haven't answered my question about what you want as an output. Possibly this:

%note that your example data doesn't have any transition from + to -
%some other example data:
data = [1 2 3 4 -5 -6 -7 -8 9 10 -11 -12 -13 -14]; 

postoneg = find(diff(sign(data)) == -2)
transitions = data([postoneg-1; postoneg; postoneg+1; postoneg+2])

[Ahmed]

Thanks, I want the output as array contains 4 point (2 negative 2 positive) For example for the first column I have

data(25,1)=[
  -0.0006662
  -0.00033225
  0.00033638
  0.001341
  0.0023478
  0.0057178
  0.012524
  0.022899
  0.033476
  0.070152
  0.15002
  0.28558
  0.43904
  1.0598
  2.6344
  5.3640
  8.2462
  18.1135
  38.0530
  68.0307
  98.0210
  198.0086
  397.9984
  698.0106
  998.0148]

I want the out put

transitions=[ -0.0006662 -0.00033225 0.00033638 0.001341]

I tried to use your code put I got empty array

[Guillaume]

Of course, you've got an empty array. You wrote I am guaranteed to always have two positive [...] before the transition and two negative [...] after. Your example is the exact opposite.

So, the question becomes, do you want positive to negative transitions as you've stated:

transitionindex = find(diff(sign(data)) == -2);

Do you want negative to positive transition as in your example:

transitionindex = find(diff(sign(data)) == 2);

Or both:

transitionindex = find(abs(diff(sign(data))) == 2);

Note that my answer applied to a row vector (as in my example). For a column vector, you need to concatenate the transition offsets horizontally instead of vertically (commas or spaces instead of semi-colons) ie:

transitions = data([transitionindex-1, transitionindex, transitionindex+1, transitionindex+2]);

Your question originally mention a matrix. You'll have to adapt the code for that as you've never explained what the output should be in that case.

[Ahmed]

Thank you so much for your help