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) .
