dplyr::filter nse

dplyrfilternse.R

library(dplyr)
library(lazyeval)
Species <- "virginica"
# The Species variable is interpreted 
# in the context of the data frame
iris %>% 
    filter_(Species == Species) %>% 
    nrow()
# 150

# The Species variable is interpreted 
# in the context of the global environment
iris %>% 
    filter_(interp(~Species == which_species, 
                   which_species = Species)) %>%
    nrow()
# 50