An Array is an immutable data array with some logical type
and some length. Most logical types are contained in the base
Array class; there are also subclasses for DictionaryArray, ListArray,
and StructArray.
The Array$create() factory method instantiates an Array and
takes the following arguments:
x: an R vector, list, or data.frame
type: an optional data type for x. If omitted, the type
will be inferred from the data.
Array$create() will return the appropriate subclass of Array, such as
DictionaryArray when given an R factor.
To compose a DictionaryArray directly, call DictionaryArray$create(),
which takes two arguments:
x: an R vector or Array of integers for the dictionary indices
dict: an R vector or Array of dictionary values (like R factor levels
but not limited to strings only)
$IsNull(i): Return true if value at index is null. Does not boundscheck
$IsValid(i): Return true if value at index is valid. Does not boundscheck
$length(): Size in the number of elements this array contains
$nbytes(): Total number of bytes consumed by the elements of the array
$offset: A relative position into another array's data, to enable zero-copy slicing
$null_count: The number of null entries in the array
$type: logical type of data
$type_id(): type id
$Equals(other) : is this array equal to other
$ApproxEquals(other) :
$Diff(other) : return a string expressing the difference between two arrays
$data(): return the underlying ArrayData
$as_vector(): convert to an R vector
$ToString(): string representation of the array
$Slice(offset, length = NULL): Construct a zero-copy slice of the array
with the indicated offset and length. If length is NULL, the slice goes
until the end of the array.
$Take(i): return an Array with values at positions given by integers
(R vector or Array Array) i.
$Filter(i, keep_na = TRUE): return an Array with values at positions where logical
vector (or Arrow boolean Array) i is TRUE.
$SortIndices(descending = FALSE): return an Array of integer positions that can be
used to rearrange the Array in ascending or descending order
$RangeEquals(other, start_idx, end_idx, other_start_idx) :
$cast(target_type, safe = TRUE, options = cast_options(safe)): Alter the
data in the array to change its type.
$View(type): Construct a zero-copy view of this array with the given type.
$Validate() : Perform any validation checks to determine obvious inconsistencies
within the array's internal data. This can be an expensive check, potentially O(length)
my_array <- Array$create(1:10)
my_array$type
#> Int32
#> int32
my_array$cast(int8())
#> Array
#> <int8>
#> [
#> 1,
#> 2,
#> 3,
#> 4,
#> 5,
#> 6,
#> 7,
#> 8,
#> 9,
#> 10
#> ]
# Check if value is null; zero-indexed
na_array <- Array$create(c(1:5, NA))
na_array$IsNull(0)
#> [1] FALSE
na_array$IsNull(5)
#> [1] TRUE
na_array$IsValid(5)
#> [1] FALSE
na_array$null_count
#> [1] 1
# zero-copy slicing; the offset of the new Array will be the same as the index passed to $Slice
new_array <- na_array$Slice(5)
new_array$offset
#> [1] 5
# Compare 2 arrays
na_array2 <- na_array
na_array2 == na_array # element-wise comparison
#> Array
#> <bool>
#> [
#> true,
#> true,
#> true,
#> true,
#> true,
#> null
#> ]
na_array2$Equals(na_array) # overall comparison
#> [1] TRUE