Build a query that counts the number of nulls in each row.
count_null_cols(source, cols, count)
incoming rel_op tree or data.frame.
character, columns to track
character, column to write count in.
rel_op node or data.frame (depending on input).
# 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(0.6, 0.5, NA),
R2 = c(1.0, 0.9, NA)))
op_tree <- d %.>% count_null_cols(., c("AUC", "R2"), "nnull")
cat(format(op_tree))
sql <- to_sql(op_tree, my_db)
cat(sql)
print(DBI::dbGetQuery(my_db, sql))
# ad-hoc mode
data.frame(AUC=c(1,NA,0.5), R2=c(NA,1,0)) %.>%
op_tree %.>%
print(.)
# cleanup
options(old_o)
DBI::dbDisconnect(my_db)
}
#> mk_td("d", c(
#> "AUC",
#> "R2")) %.>%
#> sql_node(.,
#> count_null_cols(AUC, R2))
#> SELECT
#> `R2` AS `R2`,
#> ( CASE WHEN ( `AUC` IS NULL ) THEN 1 ELSE 0 END ) + ( CASE WHEN ( `R2` IS NULL ) THEN 1 ELSE 0 END ) AS `nnull`,
#> `AUC` AS `AUC`
#> FROM (
#> SELECT
#> `AUC`,
#> `R2`
#> FROM
#> `d`
#> ) tsql_47023896753630146452_0000000000
#> R2 nnull AUC
#> 1 1.0 0 0.6
#> 2 0.9 0 0.5
#> 3 NA 2 NA
#> R2 nnull AUC
#> 1 NA 1 1.0
#> 2 1 1 NA
#> 3 0 0 0.5