# Domain and Array Operations¶

## 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 (and opaque) 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

Return true if the argument d is a rectangular domain. Otherwise return false.

proc isRectangularArr(a: []) param

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

proc isIrregularDom(d: domain) param

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

proc isIrregularArr(a: []) param

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

proc isAssociativeDom(d: domain) param

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

proc isAssociativeArr(a: []) param

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

proc isOpaqueDom(d: domain) param

Return true if d is an opaque domain. Otherwise return false.

proc isSparseDom(d: domain) param

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

proc isSparseArr(a: []) param

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

type domain

The domain type

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 enumerated 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. For a sparse domain, return the shape of the parent domain.

proc clear()

Remove all indices from this domain, leaving it empty

proc add(i)

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

The domain must be irregular.

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

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.

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. Number of indices added to the domain int
proc remove(i)

Remove index i from this domain

proc 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

proc numIndices

Return the number of indices in this domain

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 member(i: _value.idxType ...rank)

Deprecated - please use domain.contains.

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 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()

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)
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 rank param

The number of dimensions in the array

iter these() ref

Yield the array elements

proc numElements

Return the number of elements in the array

proc size

Return the number of elements in the array

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()

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 back()

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

proc push_back(in val: this.eltType)

Add element val to the back of the array, extending the array's domain by one. If the domain was {1..5} it will become {1..6}.

The array must be a rectangular 1-D array; its domain must be non-stridable and not shared with other arrays.

proc push_back(vals: [])

Extend array with elements of array vals, extending the array's domain by vals.size in the ascending direction.

The array must be a rectangular 1-D array; its domain must be non-stridable and not shared with other arrays.

proc pop_back()

Remove the last element from the array, reducing the size of the domain by one. If the domain was {1..5} it will become {1..4}

Returns the removed element.

The array must be a rectangular 1-D array; its domain must be non-stridable and not shared with other arrays.

proc front()

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

proc push_front(in val: this.eltType)

Add element val to the front of the array, extending the array's domain by one. If the domain was {1..5} it will become {0..5}.

The array must be a rectangular 1-D array; its domain must be non-stridable and not shared with other arrays.

proc push_front(vals: [])

Prepend array with elements of array vals, extending the array's domain by vals.size in the descending direction.

The array must be a rectangular 1-D array; its domain must be non-stridable and not shared with other arrays.

proc pop_front()

Remove the first element of the array reducing the size of the domain by one. If the domain was {1..5} it will become {2..5}.

Returns the removed element.

The array must be a rectangular 1-D array; its domain must be non-stridable and not shared with other arrays.

proc insert(pos: this.idxType, in val: this.eltType)

Insert element val into the array at index pos. Shift the array elements above pos up one index. If the domain was {1..5} it will become {1..6}.

The array must be a rectangular 1-D array; its domain must be non-stridable and not shared with other arrays.

proc insert(pos: this.idxType, vals: [])

Insert elements of vals into the array at index pos. Shift the array elements above pos up vals.size indices. If the domain was {1..5} and vals.size is 3,it will become {1..8}.

The array must be a rectangular 1-D array; its domain must be non-stridable and not shared with other arrays.

Aliasing arguments are not supported for this method. For example, the following call would not work as intended:

var A = [1, 2, 3, 4];
A.insert(3, A); // Will result in runtime error

proc remove(pos: this.idxType)

Remove the element at index pos from the array and shift the array elements above pos down one index. If the domain was {1..5} it will become {1..4}.

The array must be a rectangular 1-D array; its domain must be non-stridable and not shared with other arrays.

proc remove(pos: this.idxType, count: this.idxType)

Remove count elements from the array starting at index pos and shift elements above pos+count down by count indices.

The array must be a rectangular 1-D array; its domain must be non-stridable and not shared with other arrays.

proc remove(pos: range(this.idxType, stridable = false))

Remove the elements at the indices in the pos range and shift the array elements down by pos.size elements. If the domain was {1..5} and this is called with 2..3 as an argument, the new domain would be {1..3} and the array would contain the elements formerly at positions 1, 4, and 5.

The array must be a rectangular 1-D array; its domain must be non-stridable and not shared with other arrays.

proc reverse()

Reverse the order of the values in the array.

proc clear()

Remove all elements from the array leaving the domain empty. If the domain was {5..10} it will become {5..4}.

The array must be a rectangular 1-D array; its domain must be non-stridable and not shared with other arrays.

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 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.