> sample(eye.color,100,rep=T)

  [1] "bb" "aa" "cc" "dd" "cc" "cc" "bb" "dd" "cc" "cc" "dd" "bb" "cc" "dd" "cc"

 [16] "aa" "cc" "aa" "aa" "bb" "aa" "cc" "aa" "bb" "bb" "dd" "cc" "bb" "dd" "dd"

 [31] "dd" "dd" "cc" "cc" "dd" "aa" "dd" "aa" "cc" "aa" "cc" "aa" "dd" "dd" "cc"

 [46] "aa" "bb" "dd" "cc" "bb" "bb" "dd" "cc" "bb" "bb" "aa" "bb" "aa" "dd" "dd"

 [61] "aa" "aa" "aa" "cc" "bb" "aa" "cc" "bb" "bb" "bb" "aa" "bb" "dd" "aa" "aa"

 [76] "aa" "aa" "aa" "cc" "dd" "aa" "bb" "cc" "dd" "dd" "bb" "bb" "dd" "aa" "bb"

 [91] "bb" "aa" "dd" "cc" "cc" "bb" "bb" "dd" "dd" "bb"

> eyecolor<-data.frame(id=1:100,color=sample(eye.color,100,rep=T)   #sample函数获得的数据框为何下面是“+”号？

+ 

+ 

+ 

+ 

+ 

+ 

> eyecolor

Error: object 'eyecolor' not found