请看下面:

x=c("2006/10/6","2006/10/7","2006/11/2","2006/11/8")
> x=strptime(x,format="%Y/%m/%d")
> y=c("zs","zs","ls","ls")
> r=c(0.12,0.45,-0.2,0.05)
> z=data.frame(x,y,r)
> z
           x  y     r
1 2006-10-06 zs  0.12
2 2006-10-07 zs  0.45
3 2006-11-02 ls -0.20
4 2006-11-08 ls  0.05
> which(z$x=="2006-10-07"&z$y=="zs")
integer(0)
问题出在X的格式上,若

xx=c("2006/10/6","2006/10/7","2006/11/2","2006/11/8")
>
> y=c("zs","zs","ls","ls")
> r=c(0.12,0.45,-0.2,0.05)
> z=data.frame(xx,y,r)
> which(xx=="2006-10-07"&y=="zs")

>2

成功!问题解决.

但xx=="2006-10-07"有什么问题呢?

 x=strptime(x,format="%Y/%m/%d")
这一步你的参数没有用好，应该是，你可以看看 z$x，里面会有一个 "CST"，这个我就搞不懂了

你 x=as.character(strptime(x,format="%Y/%m/%d"))

就可以了