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appdevreferencedaml-standard-libraryda-list-builtinorder

DA.List.BuiltinOrder

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DA.List.BuiltinOrder

Reference documentation for Daml module DA.List.BuiltinOrder.

DA.List.BuiltinOrder

Note: This is only supported in Daml-LF 1.11 or later.

This module provides variants of other standard library

functions that are based on the builtin Daml-LF ordering rather

than user-defined ordering. This is the same order also used

by DA.Map.

These functions are usually much more efficient than their

Ord-based counterparts.

Note that the functions in this module still require Ord

constraints. This is purely to enforce that you don’t

pass in values that cannot be compared, e.g., functions. The

implementation of those instances is not used.

Module Snapshot

Stable. Status: `active` Introduced in: `3.4.9` Removed in: `-` Warnings: `0` Deprecations: `0` Deprecated since: `-`

Functions

dedup

dedup : Ord a => [a] -> [a]

dedup l removes duplicate elements from a list. In particular, it keeps only the first occurrence of each element.

dedup is stable so the elements in the output are ordered by their first occurrence in the input. If you do not need stability, consider using dedupSort which is more efficient.

>>> dedup [3, 1, 1, 3]
[3, 1]

dedupOn

dedupOn : Ord k => (v -> k) -> [v] -> [v]

A version of dedup where deduplication is done after applying the given function. Example use: dedupOn (.employeeNo) employees.

dedupOn is stable so the elements in the output are ordered by their first occurrence in the input. If you do not need stability, consider using dedupOnSort which is more efficient.

>>> dedupOn fst [(3, "a"), (1, "b"), (1, "c"), (3, "d")]
[(3, "a"), (1, "b")]

dedupSort

dedupSort : Ord a => [a] -> [a]

dedupSort is a more efficient variant of dedup that does not preserve the order of the input elements. Instead the output will be sorted acoording to the builtin Daml-LF ordering.

>>> dedupSort [3, 1, 1, 3]
[1, 3]

dedupOnSort

dedupOnSort : Ord k => (v -> k) -> [v] -> [v]

dedupOnSort is a more efficient variant of dedupOn that does not preserve the order of the input elements. Instead the output will be sorted on the values returned by the function.

For duplicates, the first element in the list will be included in the output.

>>> dedupOnSort fst [(3, "a"), (1, "b"), (1, "c"), (3, "d")]
[(1, "b"), (3, "a")]

sort

sort : Ord a => [a] -> [a]

Sort the list according to the Daml-LF ordering.

Values that are identical according to the builtin Daml-LF ordering are indistinguishable so stability is not relevant here.

>>> sort [3,1,2]
[1,2,3]

sortOn

sortOn : Ord b => (a -> b) -> [a] -> [a]

sortOn f is a version of sort that allows sorting on the result of the given function.

sortOn is stable so elements that map to the same sort key will be ordered by their position in the input.

>>> sortOn fst [(3, "a"), (1, "b"), (3, "c"), (2, "d")]
[(1, "b"), (2, "d"), (3, "a"), (3, "c")]

unique

unique : Ord a => [a] -> Bool

Returns True if and only if there are no duplicate elements in the given list.

>>> unique [1, 2, 3]
True

uniqueOn

uniqueOn : Ord k => (a -> k) -> [a] -> Bool

Returns True if and only if there are no duplicate elements in the given list after applyng function.

>>> uniqueOn fst [(1, 2), (2, 42), (1, 3)]
False

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