array-class: Array Classes

In arrow: Integration to 'Apache' 'Arrow'

Array Classes

Description

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.

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

arrow documentation built on Sept. 11, 2024, 8:02 p.m.