ex_data_table_step.relop_sql: Direct sql node.

In rqdatatable: 'rquery' for 'data.table'

Direct sql node.

Description

Execute one step using the rquery.rquery_db_executor SQL supplier. Note: it is not a good practice to use SQL nodes in data.table intended pipelines (loss of class information and cost of data transfer). This implementation is only here for completeness.

Usage

## S3 method for class 'relop_sql'
ex_data_table_step(
  optree,
  ...,
  tables = list(),
  source_usage = NULL,
  source_limit = NULL,
  env = parent.frame()
)

Arguments

optree	relop operations tree.
...	not used, force later arguments to bind by name.
tables	named list map from table names used in nodes to data.tables and data.frames.
source_usage	list mapping source table names to vectors of columns used.
source_limit	if not null limit all table sources to no more than this many rows (used for debugging).
env	environment to work in.

Examples

# WARNING: example tries to change rquery.rquery_db_executor option to RSQLite and back.
if (requireNamespace("DBI", quietly = TRUE) &&
    requireNamespace("RSQLite", quietly = TRUE)) {
  # example database connection
  my_db <- DBI::dbConnect(RSQLite::SQLite(),
                          ":memory:")
  old_o <- options(list("rquery.rquery_db_executor" = list(db = my_db)))

  # example data
  d <- data.frame(v1 = c(1, 2, NA, 3),
                  v2 = c(NA, "b", NA, "c"),
                  v3 = c(NA, NA, 7, 8),
                  stringsAsFactors = FALSE)

  # example xform
  vars <- column_names(d)
  # build a NA/NULLs per-row counting expression.
  # names are "quoted" by wrapping them with as.name().
  # constants can be quoted by an additional list wrapping.
  expr <- lapply(vars,
                 function(vi) {
                   list("+ (CASE WHEN (",
                        as.name(vi),
                        "IS NULL ) THEN 1.0 ELSE 0.0 END)")
                 })
  expr <- unlist(expr, recursive = FALSE)
  expr <- c(list(0.0), expr)

  # instantiate the operator node
  op_tree <- local_td(d) %.>%
    sql_node(., "num_missing" %:=% list(expr))
  cat(format(op_tree))

  d %.>% op_tree

  options(old_o)
  DBI::dbDisconnect(my_db)
}

rqdatatable documentation built on Aug. 21, 2023, 9:10 a.m.