na.locf但不做尾随的NA

I have the following time series

我有以下时间序列

> y<- xts(1:10, Sys.Date()+1:10)
> y[c(1,2,5,9,10)] <- NA
> y
           [,1]
2011-09-04   NA
2011-09-05   NA
2011-09-06    3
2011-09-07    4
2011-09-08   NA
2011-09-09    6
2011-09-10    7
2011-09-11    8
2011-09-12   NA
2011-09-13   NA
>