rquery (version 1.4.99)

project_se: project data by grouping, and adding aggregate columns.

Description

project data by grouping, and adding aggregate columns.

Usage

project_se(source, assignments, ..., groupby = c(), env = parent.frame())
aggregate_se(source, assignments, ..., groupby = c(), env = parent.frame())

Value

project node.

Arguments

source

source to select from.

assignments

new column assignment expressions.

...

not used, force later arguments to be by name

groupby

grouping columns.

env

environment to look for values in.

Examples

if (requireNamespace("DBI", quietly = TRUE) && requireNamespace("RSQLite", quietly = TRUE)) {
  my_db <- DBI::dbConnect(RSQLite::SQLite(),
                          ":memory:")
  d <- rq_copy_to(
    my_db, 'd',
    data.frame(group = c('a', 'a', 'b', 'b'),
               val = 1:4,
               stringsAsFactors = FALSE))

  op_tree <- d %.>%
    project_se(., groupby = "group", "vmax" %:=% "max(val)")
  cat(format(op_tree))
  sql <- to_sql(op_tree, my_db)
  cat(sql)
  execute(my_db, op_tree) %.>%
     print(.)

  op_tree <- d %.>%
    project_se(., groupby = NULL, "vmax" %:=% "max(val)")
  cat(format(op_tree))
  sql <- to_sql(op_tree, my_db)
  cat(sql)
  execute(my_db, op_tree) %.>%
     print(.)

  DBI::dbDisconnect(my_db)
}