install the ggplot2 package

Has one try to install the ggplot2 package recently? I tried to install 
it on my new system and had trouble: 

I tried a different CRAN mirror but didn't work

 library(ggplot2)
Error in loadNamespace(i, c(lib.loc, .libPaths())) : 
  there is no package called ?stringr?
In addition: Warning message:
package ?ggplot2? was built under R version 2.15.2 
Error: package/namespace load failed for ?ggplot2?



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