setkey

0th

Percentile

Create key on a data table

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.

Keywords
data
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 Do not quote the column names.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.
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.

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.

See Also

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

Aliases
  • setkey
  • key
  • key<-
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"
Documentation reproduced from package data.table, version 1.4.1, License: GPL

Community examples

raf.v.asuncion@gmail.com at Feb 27, 2018 data.table v1.10.4-2

DT = data.table(A=5:1,B=letters[5:1]) DT # before setkey(DT,B) # re-orders table and marks it sorted. DT # after