array-class function

Array Classes

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. class

Factory

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)

Usage

a <- Array$create(x)
length(a)

print(a)
a == a

Methods

• $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)

Examples

my_array <- Array$create(1:10)
my_array$type
my_array$cast(int8())

# Check if value is null; zero-indexed
na_array <- Array$create(c(1:5, NA))
na_array$IsNull(0)
na_array$IsNull(5)
na_array$IsValid(5)
na_array$null_count

# 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

# Compare 2 arrays
na_array2 <- na_array
na_array2 == na_array # element-wise comparison
na_array2$Equals(na_array) # overall comparison