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Extend data by adding more columns. — extend_se • rquery

Create a node similar to a Codd extend relational operator (add derived columns).

extend_se(
  source,
  assignments,
  ...,
  partitionby = NULL,
  orderby = NULL,
  reverse = NULL,
  display_form = NULL,
  env = parent.frame()
)

source to select from.

new column assignment expressions.

force later arguments to bind by name

partitioning (window function) terms.

ordering (in window function) terms.

reverse ordering (in window function) terms.

chacter presentation form

environment to look for values in.

extend node.

Partitionby and orderby can only be used with a database that supports window-functions (such as PostgreSQL, Spark and so on).

Note: if any window/aggregation functions are present then at least one of partitionby or orderby must be non empty. For this purpose partitionby=1 is allowed and means "single partition on the constant 1."

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(
AUC 
= 0.6
, R2 
= 0.2))
  optree <- extend_se(d
, 
c("v" %:=% "AUC + R2"
, 
"x" %:=% "pmax(AUC,v)"))
  cat(format(optree))
  sql <- to_sql(optree
, 
my_db)
  cat(sql)
  print(DBI::dbGetQuery(my_db
, 
sql))

  DBI::dbDisconnect(my_db)
}
#> mk_td("d", c(
#>   "AUC",
#>   "R2")) %.>%
#>  extend(.,
#>   v := AUC + R2) %.>%
#>  extend(.,
#>   x := pmax(AUC, v))
#> SELECT
#>  `AUC`,
#>  `R2`,
#>  `v`,
#>  ( CASE WHEN ( `AUC` ) IS NULL THEN ( `v` ) WHEN ( `v` ) IS NULL THEN ( `AUC` ) WHEN ( `AUC` ) >= ( `v` ) THEN ( `AUC` ) ELSE ( `v` ) END )  AS `x`
#> FROM (
#>  SELECT
#>   `AUC`,
#>   `R2`,
#>   `AUC` + `R2`  AS `v`
#>  FROM (
#>   SELECT
#>    `AUC`,
#>    `R2`
#>   FROM
#>    `d`
#>   ) tsql_19673537631902327278_0000000000
#>  ) tsql_19673537631902327278_0000000001
#>   AUC  R2   v   x
#> 1 0.6 0.2 0.8 0.8

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