Pass arguments to dplyr functions

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You need to use the standard evaluation versions of the dplyr functions (just append ‘_’ to the function names, ie. group_by_ & summarise_) and pass strings to your function, which you then need to turn into symbols. To parameterise the argument of summarise_, you will need to use interp(), which is defined in the lazyeval package. Concretely:

library(dplyr)
library(lazyeval)

not.uniq.per.group <- function(df, grp.var, uniq.var) {
    df %>%
        group_by_(grp.var) %>%
        summarise_( n_uniq=interp(~n_distinct(v), v=as.name(uniq.var)) ) %>%
        filter(n_uniq > 1)
}

not.uniq.per.group(iris, "Sepal.Length", "Sepal.Width")

Note that in recent versions of dplyr the standard evaluation versions of the dplyr functions have been “soft deprecated” in favor of non-standard evaluation.

See the Programming with dplyr vignette for more information on working with non-standard evaluation.

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