I have a series (l) of curves with data format,

Xa1 Ya1 Xb1 Yb1 ...... Xl1 Yl1
Xa2 Ya2 Xb2 Yb2 ...... Xl1 Yl2
.................
.................
.................
Xan Yan Xbn Ybn ...... Xln Yln

How can I get an average line with deviation ?

Xavg1 Yavg1 Dev1
Xavg2 Yavg2 Dev2
..........
..........
Xavgn Yavgn Devn

Note: Xa(i) =/= Xb(i), Ya(j) =/= Yb(j), i,j=1,n