assign_slice: Assign a value to a slice of data (set of rows meeting a...

In WinVector/rquery: Relational Query Generator for Data Manipulation at Scale

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

Description

Uses if_else_block.

Usage

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.

Details

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

Value

optree or data.frame.

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)
}

WinVector/rquery documentation built on Aug. 24, 2023, 11:12 a.m.