mean according to another column

Hi all!! I need your help please!

My data are in 4 columns:

 5,11550634065452  5,68000000000000  2,89500000000000e+18  0,000277777777777821
 5,11371667045788  5,68027777777778  4,28850000000000e+18  0,000277777777778709
 5,11237469650691  5,68055555555556  3,99960000000000e+18  0,000277777777776933
 5,11058681295688  5,68083333333333  3,56330000000000e+18  0,000277777777777821
 4,22865065482816  5,89750000000000  2,74900000000000e+18  0,216666666666667
 4,22683293766465  5,89805555555556  3,82680000000000e+18  0,000555555555555642
 4,22531743417035  5,89861111111111  3,05860000000000e+18  0,000555555555555642
 4,22380486438042  5,89916666666667  3,72440000000000e+18  0,000555555555555642
 4,22229371155370  5,89944444444445  3,42520000000000e+18  0,277777777777821
 4,22078125510264  5,90000000000000  2,90090000000000e+18  0,000555555555555642
 4,21927232883456  5,90027777777778  2,72760000000000e+18  0,000277777777776933
 4,21806586681390  5,90083333333333  3,59180000000000e+18  0,000555555555555642
 4,21655652713407  5,90138888888889  4,65340000000000e+18  0,000555555555555642

I'd like to find mean values from columns 1:3, but not from all lines. The 4th column has some lines where the number is >0.01, like the lines 5 & 9. So, I want to find the mean from lines 1-4, 5-8, and 9 until the number from 4th column is >0.01 and so on, until line 4878. (the step is not stable).

What can i do?

Thank you!

Answer 1

[Azzi Abdelmalek]

If your matrix is named a

idx=a(:,4)<=0.01
out=mean(a(idx,1:3),2)

[Thar]

The result out has more lines from the first data. It not find mean values from lines 1:4 then 5:8 and so on. Can i do anything else?

Thank you!

[Thar]

my script is:

 G=[X,X1,Y]; %airmass, time, SCD

 for k=1:4828
        G(k+1,4)=G(k+1,2)-G(k,2); %dif_time

 end

 idx=G(:,4)<=0.01;
 out=mean(G(idx,1:3),2);