I think the following codes works:

library(ggplot2)
data(diamonds)
summary(diamonds)

To see the first 5 rows of the data:

diamonds[1:5,]

我的没有问题，是不是你的ggplot2没装好


> library(ggplot2)
Loading required package: reshape
Loading required package: plyr

Attaching package: ‘reshape’

The following object(s) are masked from ‘package:plyr’:

    rename, round_any

Loading required package: grid
Loading required package: proto
> head(diamonds)
  carat       cut color clarity depth table price    x    y    z
1  0.23     Ideal     E     SI2  61.5    55   326 3.95 3.98 2.43
2  0.21   Premium     E     SI1  59.8    61   326 3.89 3.84 2.31
3  0.23      Good     E     VS1  56.9    65   327 4.05 4.07 2.31
4  0.29   Premium     I     VS2  62.4    58   334 4.20 4.23 2.63
5  0.31      Good     J     SI2  63.3    58   335 4.34 4.35 2.75
6  0.24 Very Good     J    VVS2  62.8    57   336 3.94 3.96 2.48

Hi~
data("diamonds",package="ggplot2")  
may also works~
hope that will help you~

library(ggplot2)
data(diamonds)
diamonds