6 Interval Maps

▼ |  | Data: Data Structures

1 | Imperative Queues
2 | Growable Vectors
3 | Orders and Ordered Dictionaries
4 | Splay Trees
5 | Skip Lists
6 | Interval Maps
7 | Binary Heaps
8 | Integer Sets
9 | Bit Vectors
10 | Union-Find: Sets with only Canonical Elements
11 | Enumerations

On this page:

make-interval-map
interval-map?
interval-map-ref
interval-map-set!
interval-map-update*!
interval-map-remove!
interval-map-contract!
interval-map-expand!
interval-map-cons*!
interval-map-iterate-first
interval-map-iterate-next
interval-map-iterate-key
interval-map-iterate-value
interval-map-iter?

6.8
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### 6`` Interval Maps

Ryan Culpepper <ryanc@racket-lang.org>

(require data/interval-map) | package: data-lib

An interval-map is a mutable data structure that maps half-open intervals of exact integers to values. An interval-map is queried at a discrete point, and the result of the query is the value mapped to the interval containing the point.

Internally, interval-maps use a skip-list (data/skip-list) of intervals for efficient query and update, including efficient contraction and expansion of intervals.

Interval-maps implement the dictionary (racket/dict) interface to a limited extent. Only dict-ref and the iteration-based methods (dict-iterate-first, dict-map, etc) are supported. For the iteration-based methods, the mapping’s keys are considered the pairs of the start and end positions of the mapping’s (half-open) intervals.

Examples:

> > (define r (make-interval-map))
> > (interval-map-set! r 1 5 'apple)
> > (interval-map-set! r 6 10 'pear)
> > (interval-map-set! r 3 7 'banana)
> > r
> (make-interval-map '(((1 . 3) . apple) ((3 . 7) . banana) ((7 . 10) . pear)))
> > (interval-map-ref r 1 #f)
> 'apple
> > (interval-map-ref r 3 #f)
> 'banana
> > (interval-map-ref r 10 #f)
> #f

Operations on interval-maps are not thread-safe.

> > procedure
> > (make-interval-map | [ | contents |
> > |  | #:key-contract key-contract |
> > |  | #:value-contract value-contract]) |
> → interval-map?
> | contents |  | : |  | (listof (cons/c (cons/c exact-integer? exact-integer?) any/c))
> |  |  | = |  | null
> key-contract : contract? = any/c
> value-contract : contract? = any/c

Makes a new interval-map initialized with contents, which has the form

> (list (cons (cons start end) value) ...)

Examples:

> > (define r (make-interval-map '(((0 . 5) . apple) ((5 . 10) . banana))))
> > (interval-map-ref r 2)
> 'apple
> > (interval-map-ref r 5)
> 'banana

> procedure (interval-map? v) → boolean?
> v : any/c

Returns #t if v is an interval-map, #f otherwise.

> > procedure
> > (interval-map-ref |  | interval-map |  |  |  |
> > |  | position |  |  |  |
> > | [ | default]) |  | → |  | any/c
> interval-map : interval-map?
> position : exact-integer?
> default : any/c = (lambda () (error ....))

Return the value associated with position in interval-map. If no mapping is found, default is applied if it is a procedure, or returned otherwise.

> > procedure
> > (interval-map-set! |  | interval-map |  |  |  |
> > |  | start |  |  |  |
> > |  | end |  |  |  |
> > |  | value) |  | → |  | void?
> interval-map : interval-map?
> start : exact-integer?
> end : exact-integer?
> value : any/c

Updates interval-map, associating every position in [start, end) with value.

Existing interval mappings contained in [start, end) are destroyed, and partly overlapping intervals are truncated. See interval-map-update*! for an updating procedure that preserves distinctions within [start, end).

> > procedure
> > (interval-map-update*! |  | interval-map |  |  |  |
> > |  | start |  |  |  |
> > |  | end |  |  |  |
> > |  | updater |  |  |  |
> > | [ | default]) |  | → |  | void?
> interval-map : interval-map?
> start : exact-integer?
> end : exact-integer?
> updater : (-> any/c any/c)
> default : any/c = (lambda () (error ....))

Updates interval-map, associating every position in [start, end) with the result of applying updater to the position’s previously associated value, or to the default value produced by default if no mapping exists.

Unlike interval-map-set!, interval-map-update*! preserves existing distinctions within [start, end).

> > procedure
> > (interval-map-remove! |  | interval-map |  |  |  |
> > |  | start |  |  |  |
> > |  | end) |  | → |  | void?
> interval-map : interval-map?
> start : (or/c exact-integer? -inf.0)
> end : (or/c exact-integer? +inf.0)

Removes the value associated with every position in [start, end).

> > procedure
> > (interval-map-contract! |  | interval-map |  |  |  |
> > |  | start |  |  |  |
> > |  | end) |  | → |  | void?
> interval-map : interval-map?
> start : exact-integer?
> end : exact-integer?

Contracts interval-map’s domain by removing all mappings on the interval [start, end) and decreasing intervals initally after end by (- end start).

If start is not less than end, an exception is raised.

> > procedure
> > (interval-map-expand! |  | interval-map |  |  |  |
> > |  | start |  |  |  |
> > |  | end) |  | → |  | void?
> interval-map : interval-map?
> start : exact-integer?
> end : exact-integer?

Expands interval-map’s domain by introducing a gap [start, end) and increasing intervals starting at or after start by (- end start).

If start is not less than end, an exception is raised.

> > procedure
> > (interval-map-cons*! |  | interval-map |  |  |  |
> > |  | start |  |  |  |
> > |  | end |  |  |  |
> > |  | v |  |  |  |
> > | [ | default]) |  | → |  | void?
> interval-map : interval-map?
> start : any/c
> end : any/c
> v : any/c
> default : any/c = null

Same as the following:

> (interval-map-update*! interval-map start end
> (lambda (old) (cons v old))
> default)

> procedure (interval-map-iterate-first interval-map)
> → (or/c interval-map-iter? #f)
> interval-map : interval-map?
> > procedure
> > (interval-map-iterate-next |  | interval-map |
> > |  | iter) |
> → (or/c interval-map-iter? #f)
> interval-map : interval-map?
> iter : interval-map-iter?
> > procedure
> > (interval-map-iterate-key |  | interval-map |  |  |  |
> > |  | iter) |  | → |  | pair?
> interval-map : interval-map?
> iter : interval-map-iter?
> > procedure
> > (interval-map-iterate-value |  | interval-map |  |  |  |
> > |  | iter) |  | → |  | any
> interval-map : interval-map?
> iter : interval-map-iter?

Implementations of dict-iterate-first, dict-iterate-next, dict-iterate-key, and dict-iterate-value, respectively.

> procedure (interval-map-iter? v) → boolean?
> v : any/c

Returns #t if v represents a position in an interval-map, #f otherwise.
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