indices specifying elements to extract or replace. Indices are
numeric
or character
vectors or empty (missing) or
NULL
. Numeric values are coerced to integer as by
as.integer
(and hence truncated towards zero).
Character vectors will be matched to the names
of the
object (or for matrices/arrays, the dimnames
):
see ‘Character indices’ below for further details.
For [
-indexing only: i
, j
, …
can be
logical vectors, indicating elements/slices to select. Such vectors
are recycled if necessary to match the corresponding extent.
i
, j
, …
can also be negative integers,
indicating elements/slices to leave out of the selection.
When indexing arrays by [
a single argument i
can be a
matrix with as many columns as there are dimensions of x
; the
result is then a vector with elements corresponding to the sets of
indices in each row of i
.
An index value of NULL
is treated as if it were integer(0)
.