rquery (version 0.5.0)

assign_slice: 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)

Arguments

source

optree relop node or data.frame.

testexpr

character containing the test expression.

columns

charactor vector of column names to alter.

value

value to set in matching rows and columns (scalar).

Value

optree or data.frame.

Details

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

Examples

# NOT RUN {
if (requireNamespace("DBI", quietly = TRUE) && requireNamespace("RSQLite", quietly = TRUE)) {
  # Land random selections early to avoid SQLite bug.
  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))

  # Why we need to land the random selection early
  # for SQLIte:
  q <- "SELECT r AS r1, r AS r2 FROM (
          SELECT random() AS r FROM (
             SELECT * from ( VALUES(1),(2) )
          ) a
       ) b"
  print(DBI::dbGetQuery(my_db, q))

  DBI::dbDisconnect(my_db)
}

# }