rquery (version 1.4.6)

sql_expr_set: Build a query that applies a SQL expression to a set of columns.

Description

Build a query that applies a SQL expression to a set of columns.

Usage

sql_expr_set(source, cols, expr)

Arguments

source

incoming rel_op tree or data.frame.

cols

character, columns to operate in. If a named array names are where results are landed, values names of value columns.

expr

character or list of character and names, expression to apply to columns "." stands for column value to use.

Value

rel_op node or data.frame (depending on input).

See Also

null_replace, count_null_cols, mark_null_cols

Examples

# NOT RUN {
# WARNING: example tries to change rquery.rquery_db_executor option to RSQLite and back.
if (requireNamespace("DBI", quietly = TRUE) && requireNamespace("RSQLite", quietly = TRUE)) {
  my_db <- DBI::dbConnect(RSQLite::SQLite(), ":memory:")
  RSQLite::initExtension(my_db)
  old_o <- options(list("rquery.rquery_db_executor" = list(db = my_db)))

  d <- rq_copy_to(my_db, 'd',
                   data.frame(AUC = c(NA, 0.5, NA),
                              R2 = c(1.0, 0.9, NA),
                              delta = 3,
                              cat = c("a", NA, "c"),
                              stringsAsFactors = FALSE))

  # example
  op_tree <- d %.>% sql_expr_set(., qc(AUC, R2), ". + 1")
  cat(format(op_tree))
  sql <- to_sql(op_tree, my_db)
  cat(sql)
  print(DBI::dbGetQuery(my_db, sql))

  # ex2 names (but not marked as names)
  op_tree2 <- d %.>% sql_expr_set(., qc(AUC, R2),
     ". + 1 + delta")
  cat(to_sql(op_tree2, my_db))

  # ex3 names (also so marked)
  op_tree3 <- d %.>% sql_expr_set(., qc(AUC, R2),
     list(". + 1 +", as.name("delta")))
  cat(to_sql(op_tree3, my_db))

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

# }

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