data.table (version 1.4.1)

setkey: Create key on a data table

Description

Sorts a data.table and marks it as sorted. The sorted columns are the key. The key can be any columns in any order. The columns are sorted in ascending order always.

Usage

setkey(x, ..., loc=parent.frame())
key(x)
key(x) <- value

Arguments

x

An unquoted name of a data.table.

...

The columns to sort by. Do not quote the column names. If ...is missing all the columns are used.

value

A character vector of column names.

loc

The data.table must already exist in this frame, and it is sorted by reference in this frame. loc=.GlobalEnv is often useful within functions.

Value

• No value is returned. The data.table is modified by reference. If you require a copy, take a copy first. A working copy is currently taken internally.

Details

The sort is attempted with the very fast radix method in sort.list. If that fails, the sort reverts to the default method in order. That logic is repeated column by column. If value is NULL, the key is removed.

See Also

data.table, tables, [.data.table, J

Examples

DT = data.table(A=5:1,B=letters[5:1])
    DT # before
    setkey(DT,B)  # re-orders table and marks it sorted.
    DT # after
    tables()      # KEY column reports the key'd columns
    key(DT)
    key(DT) = "A"