I am trying  to run the R command readVcf in R, it shows function not found. 
I have already downloaded the package "VariantAnnotation". I don't know if it helps.
Does anyone have any idea?
Just run these 3 command lines in R:

```
source("http://bioconductor.org/biocLite.R") 
biocLite("VariantAnnotation") #install the package
library("VariantAnnotation") #load the package
example("readVcf") #optional, test the function by running example codes
```