Rで回帰残差にNAを含める方法

> D<-data.frame(x=c(NA,2,3,4,5,6),y=c(2.1,3.2,4.9,5,6,7),residual=NA)
> Z<-lm(y~x,data=D)
> D[names(Z$residuals),"residual"]<-Z$residuals
> D
   x   y residual
1 NA 2.1       NA
2  2 3.2    -0.28
3  3 4.9     0.55
4  4 5.0    -0.22
5  5 6.0    -0.09
6  6 7.0     0.04

http://stackoverflow.com/questions/6882709/how-do-i-deal-with-nas-in-residuals-in-a-regression-in-r