Assign a value to a slice of data (set of rows meeting a condition, and specified set of columns).

Uses if_else_block.

assign_slice(source, testexpr, columns, value, env = parent.frame())

Arguments

source	optree relop node or data.frame.
testexpr	character containing the test expression.
columns	character vector of column names to alter.
value	value to set in matching rows and columns (scalar).
env	environment to look to.

Value

optree or data.frame.

Details

Note: ifebtest_* is a reserved column name for this procedure.

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(i = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10),
               a = c(0, 0, 1, 1, 1, 1, 1, 1, 1, 1),
               b = c(0, 1, 0, 1, 1, 1, 1, 1, 1, 1),
               r = runif(10)),
    temporary=TRUE, overwrite=TRUE)

  optree <- d %.>%
    assign_slice(.,
                 testexpr = qe(r<0.5),
                 columns = qc(a, b),
                 value = 2)
  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(
#>   "i",
#>   "a",
#>   "b",
#>   "r")) %.>%
#>  extend(.,
#>   ifebtest_1 := r < 0.5) %.>%
#>  extend(.,
#>   a := ifelse(ifebtest_1, 2, a),
#>   b := ifelse(ifebtest_1, 2, b)) %.>%
#>  drop_columns(.,
#>    c('ifebtest_1'))
#> SELECT
#>  `i`,
#>  `a`,
#>  `b`,
#>  `r`
#> FROM (
#>  SELECT
#>   `i`,
#>   `r`,
#>   ( CASE WHEN ( `ifebtest_1` ) THEN ( 2 ) WHEN NOT ( `ifebtest_1` ) THEN ( `a` ) ELSE NULL END )  AS `a`,
#>   ( CASE WHEN ( `ifebtest_1` ) THEN ( 2 ) WHEN NOT ( `ifebtest_1` ) THEN ( `b` ) ELSE NULL END )  AS `b`
#>  FROM (
#>   SELECT
#>    `i`,
#>    `a`,
#>    `b`,
#>    `r`,
#>    `r` < 0.5  AS `ifebtest_1`
#>   FROM (
#>    SELECT
#>     `i`,
#>     `a`,
#>     `b`,
#>     `r`
#>    FROM
#>     `d`
#>    ) tsql_52077572176947942308_0000000000
#>   ) tsql_52077572176947942308_0000000001
#> ) tsql_52077572176947942308_0000000002
#>     i a b         r
#> 1   1 0 0 0.7580536
#> 2   2 0 1 0.5325652
#> 3   3 1 0 0.5468048
#> 4   4 2 2 0.0959265
#> 5   5 2 2 0.3883498
#> 6   6 2 2 0.1723519
#> 7   7 1 1 0.6907258
#> 8   8 1 1 0.6752085
#> 9   9 1 1 0.9462948
#> 10 10 2 2 0.1962195