加载Rcpp并运行示例代码

我对R相当陌生，并且对Rcpp有问题。从此URLhttp://www.r-bloggers.com/installing-rcpp-on-windows-7-for-r-and-c-integration/我已经遵循了安装Rcpp的所有步骤。我还安装并加载了RcppClassic和Rinside。当我尝试运行建议的代码时：

# install packages
install.packages(c("Rcpp", "rbenchmark", "inline", "Runit"))
# load main two packages
library(Rcpp)
library(inline)
# do something with Rcpp to quickly check that it works
body <- '
NumericVector xx(x);
return wrap( std::accumulate( xx.begin(), xx.end(), 0.0));'
add <- cxxfunction(signature(x = "numeric"), body, plugin = "Rcpp")
x <- 1
y <- 2
res <- add(c(x, y))
res
#[1] 3

我收到以下消息：

package ‘Rcpp’ successfully unpacked and MD5 sums checked 
Warning: cannot remove prior installation of package ‘Rcpp’ package
‘rbenchmark’ successfully unpacked and MD5 sums checked package
‘inline’ successfully unpacked and MD5 sums checked 
package ‘RUnit’ successfully unpacked and MD5 sums checked
 The downloaded binary packages are in
         C:UsersRonAppDataLocalTempRtmpE3jrvodownloaded_packages 
Error in library(Rcpp) : there is no package called ‘Rcpp’

同样奇怪的是，如果我尝试使用UI并选择加载Rcpp，它不会显示为一个选项。