MATLAB: Identifying change of sign of a data and make a group for every 2 changes of sign.

change of sign

Hi, Well as my question says, i need help to make groups of data for every 2 changes of sign, for example i have this data:
0.1 -0.16966
0.2 -0.072523
0.3 0.21066
0.4 -0.06312
0.5 -0.14626
0.6 0.14327
0.7 0.010853
And i want a code that make me this following groups:
Group 1: -0.16966, -0.072523, 0.21066
Group 2: -0.06312, -0.14626, 0.14327, 0.010853
And then, find the max and min for each group, add them, find the average of all group:
G=matrix with all the groups
I have done a code which makes this but in order to work i need to put Zeros value in between of a change of sign and i have like 300 points so it takes time,
the code that i have right now is:
clear all
close all
%--------------------------OPTIMIZATION OF TMD----------------------------%
%Load files%
for u = 0:20:220;
C= strcat('TMD_',num2str(u),'.csv');
%------C=0 N*s/m------%
t0=TMD_0(:,2); %seconds%
vy0=TMD_0(:,3); %m/s%
allzeros = find(vy0 == 0);
x0 = allzeros(1:2:end);
z0 = zeros(length(x0),1);
a0 = zeros(length(x0),1);
for i=1:length(x0)-1
y0 = vy0(x0(i):1:x0(i+1));
z0(i) = max(y0);
a0(i) = min(y0);
yend0 = vy0(x0(end-1):1:x0(end));
z0(length(x0)) = max(yend0);
a(length(x0)) = min(yend0);
B0 = z0+abs(a0);
A0 = mean(B0);
Thanks for the ideas!

Best Answer

  • %generate some data for demo purpose:
    x = 0:3*360;
    data = x.*(sind(x)+cosd(2*x));
    datasign = sign(data); %get the sign of the data.
    %find where it goes from -1 to 1 or 1 to -1. Problem is there may be some 0 in between
    %so first remove the zero, but remember where everything was:
    [~, oldindices, nozerosign] = find(datasign);
    %now find the transitions in nozerosign. It's where the diff is non-null
    zerocross = find(diff(nozerosign));
    %transform the indices in nozerosign into indices in data
    zerocross = oldindices(zerocross)+1;
    %we now know where every zero crossing occurs, split the data accordingly
    splitboundaries = [1 zerocross(2:2:end) numel(data)];
    splitcount = numel(splitboundaries)-1;
    localmins = zeros(1, splitcount);
    localmaxs = zeros(1, splitcount);
    for splitidx = 1:splitcount
    splitdata = data(splitboundaries(splitidx):splitboundaries(splitidx+1));
    localmins(splitidx) = min(splitdata);
    localmaxs(splitidx) = max(splitdata);