extension methods for dplyr remote tables

dplyr_sql_extension.R

library(dplyr)
library(nycflights13)

conn <- nycflights13_sqlite()
flights_sql <- tbl(conn, 'flights')
weather_sql <- tbl(conn, 'weather')

`[.tbl_sql` <- function(x, condition) {
  x %>% select_(condition)
}

sum.tbl_sql <- function(x, na.rm = FALSE) {
  names <- colnames(x)
  if (length(names) > 1) {
    stop("sum needs a single column for remote tables")
  }
  x %>% rename_(x = as.name(names[1])) %>% summarize(sum(x)) %>% collect %>% as.numeric
}

sum(flights_sql['dep_delay'])