# Domain and Array Operations¶

Operations on Domains and Arrays.

## Distribution, Domain and Array Equality operators¶

Equality operators are defined to test if two distributions are equivalent or not:

```dist1 == dist2
dist1 != dist2
```

Or to test if two domains are equivalent or not:

```dom1 == dom2
dom1 != dom2
```

Arrays are promoted, so the result of the equality operators is an array of booleans. To get a single result use the `equals` method instead.

```arr1 == arr2 // compare each element resulting in an array of booleans
arr1 != arr2 // compare each element resulting in an array of booleans
arr1.equals(arr2) // compare entire arrays resulting in a single boolean
```

## Miscellaneous Domain and Array Operators¶

### The domain count operator `#`¶

The `#` operator can be applied to dense rectangular domains with a tuple argument whose size matches the rank of the domain (or optionally an integer in the case of a 1D domain). The operator is equivalent to applying the `#` operator to the component ranges of the domain and then using them to slice the domain.

### The array count operator `#`¶

The `#` operator can be applied to dense rectangular arrays with a tuple argument whose size matches the rank of the array (or optionally an integer in the case of a 1D array). The operator is equivalent to applying the `#` operator to the array’s domain and using the result to slice the array.

### The array swap operator `<=>`¶

The `<=>` operator can be used to swap the contents of two arrays with the same shape.

## Set Operations on Associative Domains and Arrays¶

Associative domains and arrays support a number of operators for set manipulations. The supported set operators are:

 + , | Union & Intersection - Difference ^ Symmetric Difference

Consider the following code where `A` and `B` are associative arrays:

```var C = A op B;
```

The result `C` is a new associative array backed by a new associative domain. The domains of `A` and `B` are not modified by `op`.

There are also `op=` variants that store the result into the first operand.

Consider the following code where `A` and `B` are associative arrays:

```A op= B;
```

`A` must not share its domain with another array, otherwise the program will halt with an error message.

For the `+=` and `|=` operators, the value from `B` will overwrite the existing value in `A` when indices overlap.

## Parallel Safety with respect to Arrays and Domains¶

Users must take care when applying operations to arrays and domains concurrently from distinct tasks. For instance, if one task is modifying the index set of a domain while another task is operating on either the domain itself or an array declared over that domain, this represents a race and could have arbitrary consequences including incorrect results and program crashes. While making domains and arrays safe with respect to such concurrent operations would be appealing, Chapel’s current position is that such safety guarantees would be prohibitively expensive.

Chapel arrays do support concurrent reads, writes, iterations, and operations as long as their domains are not being modified simultaneously. Such operations are subject to Chapel’s memory consistency model like any other memory accesses. Similarly, tasks may make concurrent queries and iterations on a domain as long as another task is not simultaneously modifying the domain’s index set.

By default, associative domains permit multiple tasks to modify their index sets concurrently. This adds some amount of overhead to these operations. If the user knows that all such modifications will be done serially or in a parallel-safe context, the overheads can be avoided by setting `parSafe` to `false` in the domain’s type declaration. For example, the following declaration creates an associative domain of strings where the implementation will do nothing to ensure that simultaneous modifications to the domain are parallel-safe:

```var D: domain(string, parSafe=false);
```

As with any other domain type, it is not safe to access an associative array while its domain is changing, regardless of whether `parSafe` is set to `true` or `false`.

## Functions and Methods on Arrays and Domains¶

proc isRectangularDom(d: domain) param

Warning

isRectangularDom is deprecated - please use isRectangular method on domain

proc isRectangularArr(a: []) param

Warning

isRectangularArr is deprecated - please use isRectangular method on array

proc isIrregularDom(d: domain) param

Warning

isIrregularDom is deprecated - please use isIrregular method on domain

proc isIrregularArr(a: []) param

Warning

isIrregularArr is deprecated - please use isIrregular method on array

proc isAssociativeDom(d: domain) param

Warning

isAssociativeDom is deprecated - please use isAssociative method on domain

proc isAssociativeArr(a: []) param

Warning

isAssociativeArr is deprecated - please use isAssociative method on array

proc isSparseDom(d: domain) param

Warning

isSparseDom is deprecated - please use isSparse method on domain

proc isSparseArr(a: []) param

Warning

isSparseArr is deprecated - please use isSparse method on array

type domain

The domain type

proc init(_pid: int, _instance, _unowned: bool)
proc init(value)
proc init(d: _distribution, param rank: int, type idxType = int, param stridable: bool = false, definedConst: bool = false)
proc init(d: _distribution, param rank: int, type idxType = int, param stridable: bool = false, ranges: rank*(range(idxType, BoundedRangeType.bounded, stridable)), definedConst: bool = false)
proc init(d: _distribution, type idxType, param parSafe: bool = true, definedConst: bool = false)
proc init(d: _distribution, dom: domain, definedConst: bool = false)
proc init=(const ref other: domain)
proc init=(const ref other: domain)
proc dist

Return the domain map that implements this domain

proc rank param

Return the number of dimensions in this domain

proc idxType type

Return the type of the indices of this domain

proc intIdxType type

The `idxType` as represented by an integer type. When `idxType` is an enum type, this evaluates to `int`. Otherwise, it evaluates to `idxType`.

proc stridable param

Return true if this is a stridable domain

iter these()

Yield the domain indices

proc this(i: integral ...rank)
proc dims()

Return a tuple of ranges describing the bounds of a rectangular domain. For a sparse domain, return the bounds of the parent domain.

proc dim(d: int)

Return a range representing the boundary of this domain in a particular dimension.

proc shape

Return a tuple of `intIdxType` describing the size of each dimension. Note that this routine is in the process of changing to return a tuple of `int`, similar to the `.size` query on ranges, domains, and arrays. See `ChapelRange.range.size` for details.

For a sparse domain, this returns the shape of the parent domain.

proc ref clear()

Remove all indices from this domain, leaving it empty

Add index `i` to this domain. This method is also available as the `+=` operator.

The domain must be irregular.

proc makeIndexBuffer(size: int)

Creates an index buffer which can be used for faster index addition.

```var spsDom: sparse subdomain(parentDom);
for i in someIndexIterator() do
spsDom += i;
```

You can use SparseIndexBuffer for better performance:

```var spsDom: sparse subdomain(parentDom);
var idxBuf = spsDom.makeIndexBuffer(size=N);
for i in someIndexIterator() do
idxBuf.commit();
```

The above snippet will create a buffer of size N indices, and will automatically commit indices to the sparse domain as the buffer fills up. Indices are also committed when the buffer goes out of scope.

Note

The interface and implementation is not stable and may change in the future.

Arguments

size : int – Size of the buffer in number of indices.

proc ref bulkAdd(inds: [] _value.rank*(_value.idxType), dataSorted = false, isUnique = false, preserveInds = true, addOn = nilLocale)

Adds indices in `inds` to this domain in bulk.

For sparse domains, an operation equivalent to this method is available with the `+=` operator, where the right-hand-side is an array. However, in that case, default values will be used for the flags `dataSorted`, `isUnique`, and `preserveInds`. This method is available because in some cases, expensive operations can be avoided by setting those flags. To do so, `bulkAdd` must be called explicitly (instead of `+=`).

Note

Right now, this method and the corresponding `+=` operator are only available for sparse domains. In the future, we expect that these methods will be available for all irregular domains.

Note

`nilLocale` is a sentinel value to denote that the locale where this addition should occur is unknown. We expect this to change in the future.

Arguments
• inds – Indices to be added. `inds` can be an array of `rank*idxType` or an array of `idxType` for 1-D domains.

• dataSorted : bool`true` if data in `inds` is sorted.

• isUnique : bool`true` if data in `inds` has no duplicates.

• preserveInds : bool`true` if data in `inds` needs to be preserved.

• addOn : locale – The locale where the indices should be added. Default value is `nil` which indicates that locale is unknown or there are more than one.

Returns

Number of indices added to the domain

Return type

int

proc ref remove(i)

Remove index `i` from this domain

proc ref requestCapacity(i)

Request space for a particular number of values in an domain.

Currently only applies to associative domains.

proc size

Return the number of indices in this domain. For domains whose `intIdxType != int`, please refer to the note in `ChapelRange.range.size` about changes to this routine’s return type.

proc sizeAs(type t: integral): t

Return the number of indices in this domain as the specified type

proc low

return the lowest index in this domain

proc high

Return the highest index in this domain

proc stride

Return the stride of the indices in this domain

proc alignment

Return the alignment of the indices in this domain

proc first

Return the first index in this domain

proc last

Return the last index in this domain

proc alignedLow

Return the low index in this domain factoring in alignment

proc alignedHigh

Return the high index in this domain factoring in alignment

proc contains(i: _value.idxType ...rank)

Return true if this domain contains `i`. Otherwise return false. For sparse domains, only indices with a value are considered to be contained in the domain.

proc isSubset(super: domain)

Return true if this domain is a subset of `super`. Otherwise returns false.

proc isSuper(sub: domain)

Return true if this domain is a superset of `sub`. Otherwise returns false.

proc orderToIndex(order: int)

Returns the ith index in the domain counting from 0. For example, `{2..10 by 2}.orderToIndex(2)` would return `6`.

The order of a multidimensional domain follows its serial iterator. For example, `{1..3, 1..2}.orderToIndex(3)` would return `(2, 2)`.

Note

Right now, this method supports only dense rectangular domains with numeric indices

Arguments

order – Order for which the corresponding index in the domain has to be found.

Returns

Domain index for a given order in the domain.

proc expand(off: rank*(intIdxType))

Return a new domain that is the current domain expanded by `off(d)` in dimension `d` if `off(d)` is positive or contracted by `off(d)` in dimension `d` if `off(d)` is negative.

proc expand(off: intIdxType)

Return a new domain that is the current domain expanded by `off` in all dimensions if `off` is positive or contracted by `off` in all dimensions if `off` is negative.

proc exterior(off: rank*(intIdxType))

Return a new domain that is the exterior portion of the current domain with `off(d)` indices for each dimension `d`. If `off(d)` is negative, compute the exterior from the low bound of the dimension; if positive, compute the exterior from the high bound.

proc exterior(off: intIdxType)

Return a new domain that is the exterior portion of the current domain with `off` indices for each dimension. If `off` is negative, compute the exterior from the low bound of the dimension; if positive, compute the exterior from the high bound.

proc interior(off: rank*(intIdxType))

Return a new domain that is the interior portion of the current domain with `off(d)` indices for each dimension `d`. If `off(d)` is negative, compute the interior from the low bound of the dimension; if positive, compute the interior from the high bound.

proc interior(off: intIdxType)

Return a new domain that is the interior portion of the current domain with `off` indices for each dimension. If `off` is negative, compute the interior from the low bound of the dimension; if positive, compute the interior from the high bound.

proc translate(off)

Return a new domain that is the current domain translated by `off(d)` in each dimension `d`.

proc translate(off)

Return a new domain that is the current domain translated by `off` in each dimension.

proc isEmpty(): bool

Return true if the domain has no indices

proc localSlice(r ...rank)

Return a local view of the sub-array (slice) defined by the provided range(s), halting if the slice contains elements that are not local.

Indexing into this local view is cheaper, because the indices are known to be local.

proc localSlice(d: domain)

Return a local view of the sub-array (slice) defined by the provided domain, halting if the slice contains elements that are not local.

Indexing into this local view is cheaper, because the indices are known to be local.

iter sorted(comparator: ?t = chpl_defaultComparator())

Yield the domain indices in sorted order

proc safeCast(type t: domain)

Cast a rectangular domain to another rectangular domain type. If the old type is stridable and the new type is not stridable, ensure that the stride was 1.

proc targetLocales() const ref

Return an array of locales over which this domain has been distributed.

proc hasSingleLocalSubdomain() param

Return true if the local subdomain can be represented as a single domain. Otherwise return false.

proc localSubdomain(loc: locale = here)

Return the subdomain that is local to loc.

Arguments

loc : locale – indicates the locale for which the query should take place (defaults to here)

iter localSubdomains(loc: locale = here)

Yield the subdomains that are local to loc.

Arguments

loc : locale – indicates the locale for which the query should take place (defaults to here)

proc isRectangular() param

Return true if this domain is a rectangular. Otherwise return false.

proc isIrregular() param

Return true if `d` is an irregular domain; e.g. is not rectangular. Otherwise return false.

proc isAssociative() param

Return true if `d` is an associative domain. Otherwise return false.

proc isSparse() param

Return true if `d` is a sparse domain. Otherwise return false.

type array

The array type

proc eltType type

The type of elements contained in the array

proc idxType type

The type of indices used in the array’s domain

proc intIdxType type
proc rank param

The number of dimensions in the array

proc indices

Return the array’s indices as a copy of its domain.

Note

In a forthcoming release, we expect `.indices` to change in behavior to return/yield indices using a local representation rather than as a clone of the array’s domain. In order to preserve the legacy behavior in your program, please use `.domain` instead (or a copy thereof).

If you’d like to opt into a prototype of the new behavior, recompile with `-sarrayIndicesAlwaysLocal=true`. For dense, rectangular arrays, this will have the effect of returning a local domain representing the array’s indices; for a sparse or associative array, it will invoke a serial iterator that yields the array’s indices.

See https://github.com/chapel-lang/chapel/issues/17883 for further details.

Warning

the current behavior of ‘.indices’ on arrays is deprecated; see https://chapel-lang.org/docs/1.25/builtins/ChapelArray.html#ChapelArray.indices for details

proc dims()

Return a tuple of ranges describing the bounds of a rectangular domain. For a sparse domain, return the bounds of the parent domain.

proc dim(d: int)

Return a range representing the boundary of this domain in a particular dimension.

iter these() ref

Yield the array elements

proc size

Return the number of elements in the array

proc sizeAs(type t: integral)

Return the number of elements in the array as the specified type.

proc reindex(newDomain: domain)

Return an array view over a new domain. The new domain must be of the same rank and size as the original array’s domain.

For example:

```var A: [1..10] int;
const D = {6..15};
ref reA = A.reindex(D);
reA[6] = 1; // updates A[1]
```
proc reindex(newDims ...)

Return an array view over a new domain defined implicitly by one or more newDims, which must be ranges. The new domain must be of the same rank and size as the original array’s domain.

For example:

```var A: [3..4, 5..6] int;
ref reA = A.reindex(13..14, 15..16);
reA[13,15] = 1; // updates A[3,5]
```
proc IRV

Return the Implicitly Represented Value for sparse arrays

iter sorted(comparator: ?t = chpl_defaultComparator())

Yield the array elements in sorted order.

proc targetLocales() const ref

Return an array of locales over which this array has been distributed.

proc hasSingleLocalSubdomain() param

Return true if the local subdomain can be represented as a single domain. Otherwise return false.

proc localSubdomain(loc: locale = here)

Return the subdomain that is local to loc.

Arguments

loc : locale – indicates the locale for which the query should take place (defaults to here)

iter localSubdomains(loc: locale = here)

Yield the subdomains that are local to loc.

Arguments

loc : locale – indicates the locale for which the query should take place (defaults to here)

proc isEmpty(): bool

Return true if the array has no elements

proc last

Return the last element in the array. The array must be a rectangular 1-D array.

proc back()

Warning

Array back() method is deprecated; use `last` instead

proc first

Return the first element in the array. The array must be a rectangular 1-D array.

proc front()

Warning

Array front() method is deprecated; use `first` instead

proc reverse()

Reverse the order of the values in the array.

proc find(val: this.eltType): (bool, index(this.domain))

Return a tuple containing `true` and the index of the first instance of `val` in the array, or if `val` is not found, a tuple containing `false` and an unspecified value is returned.

proc count(val: this.eltType): int

Return the number of times `val` occurs in the array.

proc shape

Return a tuple of integers describing the size of each dimension. For a sparse array, returns the shape of the parent domain.

proc isRectangular() param

Return true if the argument `a` is an array with a rectangular domain. Otherwise return false.

proc isIrregular() param

Return true if `a` is an array with an irregular domain; e.g. not rectangular. Otherwise return false.

proc isAssociative() param

Return true if `a` is an array with an associative domain. Otherwise return false.

proc isSparse() param

Return true if `a` is an array with a sparse domain. Otherwise return false.

proc array.equals(that: []): bool

Return true if all this array is the same size and shape as argument `that` and all elements of this array are equal to the corresponding element in `that`. Otherwise return false.

proc isDmapType(type t) param

Return true if `t` is a domain map type. Otherwise return false.

proc isDmapValue(e) param

Return true if `e` is a domain map. Otherwise return false.

proc isDomainType(type t) param

Return true if `t` is a domain type. Otherwise return false.

proc isDomainValue(e) param

Return true if `e` is a domain. Otherwise return false.

proc isArrayType(type t) param

Return true if `t` is an array type. Otherwise return false.

proc isArrayValue(e) param

Return true if `e` is an array. Otherwise return false.

proc reshape(A: [], D: domain)

Return a copy of the array `A` containing the same values but in the shape of the domain `D`. The number of indices in the domain must equal the number of elements in the array. The elements of `A` are copied into the new array using the default iteration orders over `D` and `A`.