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std.algorithm.comparison
This is a submodule of std.algorithm.
It contains generic comparison algorithms.
Function Name | Description |
---|---|
among | Checks if a value is among a set of values, e.g. if (v.among(1, 2, 3)) // v is 1, 2 or 3 |
castSwitch | (new A()).castSwitch((A a)=>1,(B b)=>2) returns 1. |
clamp | clamp(1, 3, 6) returns 3. clamp(4, 3, 6) returns 4. |
cmp | cmp("abc", "abcd") is -1, cmp("abc", "aba") is 1, and cmp("abc", "abc") is 0. |
either | Return first parameter p that passes an if (p) test, e.g. either(0, 42, 43) returns 42. |
equal | Compares ranges for element-by-element equality, e.g. equal([1, 2, 3], [1.0, 2.0, 3.0]) returns true. |
isPermutation | isPermutation([1, 2], [2, 1]) returns true. |
isSameLength | isSameLength([1, 2, 3], [4, 5, 6]) returns true. |
levenshteinDistance | levenshteinDistance("kitten", "sitting") returns 3 by using the Levenshtein distance algorithm. |
levenshteinDistanceAndPath | levenshteinDistanceAndPath("kitten", "sitting") returns tuple(3, "snnnsni") by using the Levenshtein distance algorithm. |
max | max(3, 4, 2) returns 4. |
min | min(3, 4, 2) returns 2. |
mismatch | mismatch("oh hi", "ohayo") returns tuple(" hi", "ayo"). |
predSwitch | 2.predSwitch(1, "one", 2, "two", 3, "three") returns "two". |
License:
Authors:
Source std/algorithm/comparison.d
- uint
among
(alias pred = (a, b) => a == b, Value, Values...)(Valuevalue
, Valuesvalues
)
if (Values.length != 0);
templateamong
(values...) if (isExpressionTuple!values) - Find
value
amongvalues
, returning the 1-based index of the first matching value invalues
, or 0 ifvalue
is not amongvalues
. The predicate pred is used to compare values, and uses equality by default.Parameters:pred The predicate used to compare the values. Value value
The value to search for. Values values
The values to compare the value to. Returns:0 if value was not found among the values, otherwise the index of the found value plus one is returned.Examples:assert(3.among(1, 42, 24, 3, 2)); if (auto pos = "bar".among("foo", "bar", "baz")) writeln(pos); // 2 else assert(false); // 42 is larger than 24 writeln(42.among!((lhs, rhs) => lhs > rhs)(43, 24, 100)); // 2
Examples:Alternatively,values
can be passed at compile-time, allowing for a more efficient search, but one that only supports matching on equality:assert(3.among!(2, 3, 4)); writeln("bar".among!("foo", "bar", "baz")); // 2
- auto
castSwitch
(choices...)(ObjectswitchObject
); - Executes and returns one of a collection of handlers based on the type of the switch object.The first choice that
switchObject
can be casted to the type of argument it accepts will be called withswitchObject
casted to that type, and the value it'll return will be returned bycastSwitch
. If a choice's return type is void, the choice must throw an exception, unless all the choices are void. In that case, castSwitch itself will return void.Throws:If none of the choice matches, a SwitchError will be thrown. SwitchError will also be thrown if not all the choices are void and a void choice was executed without throwing anything.Parameters:choices The choices needs to be composed of function or delegate handlers that accept one argument. There can also be a choice that accepts zero arguments. That choice will be invoked if the switchObject is null. Object switchObject
the object against which the tests are being made. Returns:The value of the selected choice.Note
castSwitch
can only be used with object types.Examples:import std.algorithm.iteration : map; import std.format : format; class A { int a; this(int a) {this.a = a;} @property int i() { return a; } } interface I { } class B : I { } Object[] arr = [new A(1), new B(), null]; auto results = arr.map!(castSwitch!( (A a) => "A with a value of %d".format(a.a), (I i) => "derived from I", () => "null reference", ))(); // A is handled directly: writeln(results[0]); // "A with a value of 1" // B has no handler - it is handled by the handler of I: writeln(results[1]); // "derived from I" // null is handled by the null handler: writeln(results[2]); // "null reference"
Examples:Using with void handlers:import std.exception : assertThrown; class A { } class B { } // Void handlers are allowed if they throw: assertThrown!Exception( new B().castSwitch!( (A a) => 1, (B d) { throw new Exception("B is not allowed!"); } )() ); // Void handlers are also allowed if all the handlers are void: new A().castSwitch!( (A a) { }, (B b) { assert(false); }, )();
- auto
clamp
(T1, T2, T3)(T1val
, T2lower
, T3upper
)
if (is(typeof(max(min(val
,upper
),lower
)))); - Clamps a value into the given bounds.This function is equivalent to max(
lower
, min(upper
,val
)).Parameters:T1 val
The value to clamp. T2 lower
The lower bound of the clamp. T3 upper
The upper bound of the clamp. Returns:Returnsval
, if it is betweenlower
andupper
. Otherwise returns the nearest of the two.Examples:writeln(clamp(2, 1, 3)); // 2 writeln(clamp(0, 1, 3)); // 1 writeln(clamp(4, 1, 3)); // 3 writeln(clamp(1, 1, 1)); // 1 writeln(clamp(5, -1, 2u)); // 2
- auto
cmp
(R1, R2)(R1r1
, R2r2
)
if (isInputRange!R1 && isInputRange!R2);
intcmp
(alias pred, R1, R2)(R1r1
, R2r2
)
if (isInputRange!R1 && isInputRange!R2); - Performs a lexicographical comparison on two input ranges. Iterating
r1
andr2
in lockstep,cmp
compares each element e1 ofr1
with the corresponding element e2 inr2
. If one of the ranges has been finished,cmp
returns a negative value ifr1
has fewer elements thanr2
, a positive value ifr1
has more elements thanr2
, and 0 if the ranges have the same number of elements.If the ranges are strings,cmp
performs UTF decoding appropriately and compares the ranges one code point at a time. A custom predicate may be specified, in which casecmp
performs a three-way lexicographical comparison using pred. Otherwise the elements are compared using opCmp.Parameters:pred Predicate used for comparison. Without a predicate specified the ordering implied by opCmp is used. R1 r1
The first range. R2 r2
The second range. Returns:0 if the ranges compare equal. A negative value ifr1
is a prefix ofr2
or the first differing element ofr1
is less than the corresponding element ofr2
according to pred. A positive value ifr2
is a prefix ofr1
or the first differing element ofr2
is less than the corresponding element ofr1
according to pred.Note An earlier version of the documentation incorrectly stated that -1 is the only negative value returned and 1 is the only positive value returned. Whether that is true depends on the types being compared.
Examples:int result; result = cmp("abc", "abc"); writeln(result); // 0 result = cmp("", ""); writeln(result); // 0 result = cmp("abc", "abcd"); assert(result < 0); result = cmp("abcd", "abc"); assert(result > 0); result = cmp("abc"d, "abd"); assert(result < 0); result = cmp("bbc", "abc"w); assert(result > 0); result = cmp("aaa", "aaaa"d); assert(result < 0); result = cmp("aaaa", "aaa"d); assert(result > 0); result = cmp("aaa", "aaa"d); writeln(result); // 0 result = cmp("aaa"d, "aaa"d); writeln(result); // 0 result = cmp(cast(int[])[], cast(int[])[]); writeln(result); // 0 result = cmp([1, 2, 3], [1, 2, 3]); writeln(result); // 0 result = cmp([1, 3, 2], [1, 2, 3]); assert(result > 0); result = cmp([1, 2, 3], [1L, 2, 3, 4]); assert(result < 0); result = cmp([1L, 2, 3], [1, 2]); assert(result > 0);
Examples:Example predicate that compares individual elements in reverse lexical orderint result; result = cmp!"a > b"("abc", "abc"); writeln(result); // 0 result = cmp!"a > b"("", ""); writeln(result); // 0 result = cmp!"a > b"("abc", "abcd"); assert(result < 0); result = cmp!"a > b"("abcd", "abc"); assert(result > 0); result = cmp!"a > b"("abc"d, "abd"); assert(result > 0); result = cmp!"a > b"("bbc", "abc"w); assert(result < 0); result = cmp!"a > b"("aaa", "aaaa"d); assert(result < 0); result = cmp!"a > b"("aaaa", "aaa"d); assert(result > 0); result = cmp!"a > b"("aaa", "aaa"d); writeln(result); // 0 result = cmp("aaa"d, "aaa"d); writeln(result); // 0 result = cmp!"a > b"(cast(int[])[], cast(int[])[]); writeln(result); // 0 result = cmp!"a > b"([1, 2, 3], [1, 2, 3]); writeln(result); // 0 result = cmp!"a > b"([1, 3, 2], [1, 2, 3]); assert(result < 0); result = cmp!"a > b"([1, 2, 3], [1L, 2, 3, 4]); assert(result < 0); result = cmp!"a > b"([1L, 2, 3], [1, 2]); assert(result > 0);
- template
equal
(alias pred = "a == b") - Compares two ranges for equality, as defined by predicate pred (which is == by default).Examples:
import std.algorithm.comparison : equal; import std.math.operations : isClose; int[4] a = [ 1, 2, 4, 3 ]; assert(!equal(a[], a[1..$])); assert(equal(a[], a[])); assert(equal!((a, b) => a == b)(a[], a[])); // different types double[4] b = [ 1.0, 2, 4, 3]; assert(!equal(a[], b[1..$])); assert(equal(a[], b[])); // predicated: ensure that two vectors are approximately equal double[4] c = [ 1.0000000005, 2, 4, 3]; assert(equal!isClose(b[], c[]));
Examples:Tip:equal
can itself be used as a predicate to other functions. This can be very useful when the element type of a range is itself a range. In particular,equal
can be its own predicate, allowing range of range (of range...) comparisons.import std.algorithm.comparison : equal; import std.range : iota, chunks; assert(equal!(equal!equal)( [[[0, 1], [2, 3]], [[4, 5], [6, 7]]], iota(0, 8).chunks(2).chunks(2) ));
- bool
equal
(Range1, Range2)(Range1r1
, Range2r2
)
if (isInputRange!Range1 && isInputRange!Range2 && !(isInfinite!Range1 && isInfinite!Range2) && is(typeof(binaryFun!pred(r1
.front,r2
.front)))); - Compares two ranges for equality. The ranges may have different element types, as long as pred(
r1
.front,r2
.front) evaluates to bool. Performs Ο(min(r1.length, r2.length)) evaluations of pred.At least one of the ranges must be finite. If one range involved is infinite, the result is (statically known to be) false. If the two ranges are different kinds of UTF code unit (char, wchar, or dchar), then the arrays are compared using UTF decoding to avoid accidentally integer-promoting units.Parameters:Range1 r1
The first range to be compared. Range2 r2
The second range to be compared. Returns:true if and only if the two ranges compare equal element for element, according to binary predicate pred.
- enum
EditOp
: char; - Encodes edit operations necessary to transform one sequence into another. Given sequences s (source) and t (target), a sequence of
EditOp
encodes the steps that need to be taken to convert s into t. For example, if s = "cat" and "cars", the minimal sequence that transforms s into t is: skip two characters, replace 't' with 'r', and insert an 's'. Working with edit operations is useful in applications such as spell-checkers (to find the closest word to a given misspelled word), approximate searches, diff-style programs that compute the difference between files, efficient encoding of patches, DNA sequence analysis, and plagiarism detection.Examples:with(EditOp) { // [none, none, none, insert, insert, insert] writeln(levenshteinDistanceAndPath("foo", "foobar")[1]); // [substitute, none, substitute, none, none, remove] writeln(levenshteinDistanceAndPath("banana", "fazan")[1]); }
none
- Current items are equal; no editing is necessary.
substitute
- Substitute current item in target with current item in source.
insert
- Insert current item from the source into the target.
remove
- Remove current item from the target.
- size_t
levenshteinDistance
(alias equals = (a, b) => a == b, Range1, Range2)(Range1s
, Range2t
)
if (isForwardRange!Range1 && isForwardRange!Range2);
size_tlevenshteinDistance
(alias equals = (a, b) => a == b, Range1, Range2)(auto ref Range1s
, auto ref Range2t
)
if (isConvertibleToString!Range1 || isConvertibleToString!Range2); - Returns the Levenshtein distance between
s
andt
. The Levenshtein distance computes the minimal amount of edit operations necessary to transforms
intot
. Performs Ο(s.length * t.length) evaluations of equals and occupies Ο(min(s.length, t.length)) storage.Parameters:equals The binary predicate to compare the elements of the two ranges. Range1 s
The original range. Range2 t
The transformation target Returns:The minimal number of edits to transform s into t. Does not allocate GC memory.Examples:import std.algorithm.iteration : filter; import std.uni : toUpper; writeln(levenshteinDistance("cat", "rat")); // 1 writeln(levenshteinDistance("parks", "spark")); // 2 writeln(levenshteinDistance("abcde", "abcde")); // 0 writeln(levenshteinDistance("abcde", "abCde")); // 1 writeln(levenshteinDistance("kitten", "sitting")); // 3 assert(levenshteinDistance!((a, b) => toUpper(a) == toUpper(b)) ("parks", "SPARK") == 2); writeln(levenshteinDistance("parks".filter!"true", "spark".filter!"true")); // 2 writeln(levenshteinDistance("ID", "I♥D")); // 1
- Tuple!(size_t, EditOp[])
levenshteinDistanceAndPath
(alias equals = (a, b) => a == b, Range1, Range2)(Range1s
, Range2t
)
if (isForwardRange!Range1 && isForwardRange!Range2);
Tuple!(size_t, EditOp[])levenshteinDistanceAndPath
(alias equals = (a, b) => a == b, Range1, Range2)(auto ref Range1s
, auto ref Range2t
)
if (isConvertibleToString!Range1 || isConvertibleToString!Range2); - Returns the Levenshtein distance and the edit path between
s
andt
.Parameters:equals The binary predicate to compare the elements of the two ranges. Range1 s
The original range. Range2 t
The transformation target Returns:Tuple with the first element being the minimal amount of edits to transform s into t and the second element being the sequence of edits to effect this transformation. Allocates GC memory for the returned EditOp[] array.Examples:string a = "Saturday", b = "Sundays"; auto p = levenshteinDistanceAndPath(a, b); writeln(p[0]); // 4 assert(equal(p[1], "nrrnsnnni"));
- auto
max
(T...)(Targs
)
if (T.length >= 2 && !is(CommonType!T == void)); - Iterates the passed arguments and returns the maximum value.Parameters:
T args
The values to select the maximum from. At least two arguments must be passed, and they must be comparable with >. Returns:The maximum of the passed-in values. The type of the returned value is the type among the passed arguments that is able to store the largest value. If at least one of the arguments is NaN, the result is an unspecified value. See std.algorithm.searching.maxElement for examples on how to cope with NaNs.See Also:Examples:int a = 5; short b = 6; double c = 2; auto d = max(a, b); assert(is(typeof(d) == int)); writeln(d); // 6 auto e = min(a, b, c); assert(is(typeof(e) == double)); writeln(e); // 2
- auto
min
(T...)(Targs
)
if (T.length >= 2 && !is(CommonType!T == void)); - Iterates the passed arguments and returns the minimum value.Parameters:
T args
The values to select the minimum from. At least two arguments must be passed, and they must be comparable with <. Returns:The minimum of the passed-in values. The type of the returned value is the type among the passed arguments that is able to store the smallest value. If at least one of the arguments is NaN, the result is an unspecified value. See std.algorithm.searching.minElement for examples on how to cope with NaNs.See Also:Examples:int a = 5; short b = 6; double c = 2; auto d = min(a, b); static assert(is(typeof(d) == int)); writeln(d); // 5 auto e = min(a, b, c); static assert(is(typeof(e) == double)); writeln(e); // 2 ulong f = 0xffff_ffff_ffff; const uint g = min(f, 0xffff_0000); writeln(g); // 0xffff_0000 dchar h = 100; uint i = 101; static assert(is(typeof(min(h, i)) == dchar)); static assert(is(typeof(min(i, h)) == uint)); writeln(min(h, i)); // 100
Examples:With arguments of mixed signedness, the return type is the one that can store the lowest values.int a = -10; uint f = 10; static assert(is(typeof(min(a, f)) == int)); writeln(min(a, f)); // -10
Examples:User-defined types that support comparison with < are supported.import std.datetime; writeln(min(Date(2012, 12, 21), Date(1982, 1, 4))); // Date(1982, 1, 4) writeln(min(Date(1982, 1, 4), Date(2012, 12, 21))); // Date(1982, 1, 4) writeln(min(Date(1982, 1, 4), Date.min)); // Date.min writeln(min(Date.min, Date(1982, 1, 4))); // Date.min writeln(min(Date(1982, 1, 4), Date.max)); // Date(1982, 1, 4) writeln(min(Date.max, Date(1982, 1, 4))); // Date(1982, 1, 4) writeln(min(Date.min, Date.max)); // Date.min writeln(min(Date.max, Date.min)); // Date.min
- Tuple!(Range1, Range2)
mismatch
(alias pred = "a == b", Range1, Range2)(Range1r1
, Range2r2
)
if (isInputRange!Range1 && isInputRange!Range2); - Sequentially compares elements in
r1
andr2
in lockstep, and stops at the first mismatch (according to pred, by default equality). Returns a tuple with the reduced ranges that start with the two mismatched values. Performs Ο(min(r1.length, r2.length)) evaluations of pred.Examples:int[6] x = [ 1, 5, 2, 7, 4, 3 ]; double[6] y = [ 1.0, 5, 2, 7.3, 4, 8 ]; auto m = mismatch(x[], y[]); writeln(m[0]); // x[3 .. $] writeln(m[1]); // y[3 .. $]
- auto
predSwitch
(alias pred = "a == b", T, R...)(TswitchExpression
, lazy Rchoices
); - Returns one of a collection of expressions based on the value of the switch expression.
choices
needs to be composed of pairs of test expressions and return expressions. Each test-expression is compared withswitchExpression
using pred(switchExpression
is the first argument) and if that yields true - the return expression is returned. Both the test and the return expressions are lazily evaluated.Parameters:T switchExpression
The first argument for the predicate. R choices
Pairs of test expressions and return expressions. The test expressions will be the second argument for the predicate, and the return expression will be returned if the predicate yields true with switchExpression and the test expression as arguments. May also have a default return expression, that needs to be the last expression without a test expression before it. A return expression may be of void type only if it always throws. Returns:The return expression associated with the first test expression that made the predicate yield true, or the default return expression if no test expression matched.Throws:If there is no default return expression and the predicate does not yield true with any test expression - SwitchError is thrown. SwitchError is also thrown if a void return expression was executed without throwing anything.Examples:string res = 2.predSwitch!"a < b"( 1, "less than 1", 5, "less than 5", 10, "less than 10", "greater or equal to 10"); writeln(res); // "less than 5" //The arguments are lazy, which allows us to use predSwitch to create //recursive functions: int factorial(int n) { return n.predSwitch!"a <= b"( -1, {throw new Exception("Can not calculate n! for n < 0");}(), 0, 1, // 0! = 1 n * factorial(n - 1) // n! = n * (n - 1)! for n >= 0 ); } writeln(factorial(3)); // 6 //Void return expressions are allowed if they always throw: import std.exception : assertThrown; assertThrown!Exception(factorial(-9));
- bool
isSameLength
(Range1, Range2)(Range1r1
, Range2r2
)
if (isInputRange!Range1 && isInputRange!Range2); - Checks if the two ranges have the same number of elements. This function is optimized to always take advantage of the length member of either range if it exists.If both ranges have a length member, this function is Ο(1). Otherwise, this function is Ο(min(r1.length, r2.length)). Infinite ranges are considered of the same length. An infinite range has never the same length as a finite range.Parameters:
Range1 r1
a finite input range Range2 r2
a finite input range Returns:true if both ranges have the same length, false otherwise.Examples:assert(isSameLength([1, 2, 3], [4, 5, 6])); assert(isSameLength([0.3, 90.4, 23.7, 119.2], [42.6, 23.6, 95.5, 6.3])); assert(isSameLength("abc", "xyz")); int[] a; int[] b; assert(isSameLength(a, b)); assert(!isSameLength([1, 2, 3], [4, 5])); assert(!isSameLength([0.3, 90.4, 23.7], [42.6, 23.6, 95.5, 6.3])); assert(!isSameLength("abcd", "xyz"));
- bool
isPermutation
(Flag!"allocateGC" allocateGC, Range1, Range2)(Range1r1
, Range2r2
)
if (allocateGC == Yes.allocateGC && isForwardRange!Range1 && isForwardRange!Range2 && !isInfinite!Range1 && !isInfinite!Range2);
boolisPermutation
(alias pred = "a == b", Range1, Range2)(Range1r1
, Range2r2
)
if (is(typeof(binaryFun!pred)) && isForwardRange!Range1 && isForwardRange!Range2 && !isInfinite!Range1 && !isInfinite!Range2); - Checks if both ranges are permutations of each other.This function can allocate if the Yes.allocateGC flag is passed. This has the benefit of have better complexity than the Yes.allocateGC option. However, this option is only available for ranges whose equality can be determined via each element's toHash method. If customized equality is needed, then the pred template parameter can be passed, and the function will automatically switch to the non-allocating algorithm. See std.functional.binaryFun for more details on how to define pred. Non-allocating forward range option: Ο(n^2) Non-allocating forward range option with custom pred: Ο(n^2) Allocating forward range option: amortized Ο(r1.length) + Ο(r2.length)Parameters:
pred an optional parameter to change how equality is defined allocateGC Yes.allocateGC/No.allocateGC Range1 r1
A finite forward range Range2 r2
A finite forward range Returns:true if all of the elements inr1
appear the same number of times inr2
. Otherwise, returns false.Examples:import std.typecons : Yes; assert(isPermutation([1, 2, 3], [3, 2, 1])); assert(isPermutation([1.1, 2.3, 3.5], [2.3, 3.5, 1.1])); assert(isPermutation("abc", "bca")); assert(!isPermutation([1, 2], [3, 4])); assert(!isPermutation([1, 1, 2, 3], [1, 2, 2, 3])); assert(!isPermutation([1, 1], [1, 1, 1])); // Faster, but allocates GC handled memory assert(isPermutation!(Yes.allocateGC)([1.1, 2.3, 3.5], [2.3, 3.5, 1.1])); assert(!isPermutation!(Yes.allocateGC)([1, 2], [3, 4]));
- CommonType!(T, Ts)
either
(alias pred = (a) => a, T, Ts...)(Tfirst
, lazy Tsalternatives
)
if (alternatives
.length >= 1 && !is(CommonType!(T, Ts) == void) && allSatisfy!(ifTestable, T, Ts)); - Get the first argument a that passes an if (unaryFun!pred(a)) test. If no argument passes the test, return the last argument.Similar to behaviour of the or operator in dynamic languages such as Lisp's (or ...) and Python's a or b or ... except that the last argument is returned upon no match. Simplifies logic, for instance, in parsing rules where a set of alternative matchers are tried. The first one that matches returns it match result, typically as an abstract syntax tree (AST).Bugs:Lazy parameters are currently, too restrictively, inferred by DMD to always throw even though they don't need to be. This makes it impossible to currently mark
either
as nothrow. See issue at Bugzilla 12647.Returns:The first argument that passes the test pred.Examples:const a = 1; const b = 2; auto ab = either(a, b); static assert(is(typeof(ab) == const(int))); writeln(ab); // a auto c = 2; const d = 3; auto cd = either!(a => a == 3)(c, d); // use predicate static assert(is(typeof(cd) == int)); writeln(cd); // d auto e = 0; const f = 2; auto ef = either(e, f); static assert(is(typeof(ef) == int)); writeln(ef); // f
Examples:immutable p = 1; immutable q = 2; auto pq = either(p, q); static assert(is(typeof(pq) == immutable(int))); writeln(pq); // p writeln(either(3, 4)); // 3 writeln(either(0, 4)); // 4 writeln(either(0, 0)); // 0 writeln(either("", "a")); // ""
Examples:string r = null; writeln(either(r, "a")); // "a" writeln(either("a", "")); // "a" immutable s = [1, 2]; writeln(either(s, s)); // s writeln(either([0, 1], [1, 2])); // [0, 1] writeln(either([0, 1], [1])); // [0, 1] writeln(either("a", "b")); // "a" static assert(!__traits(compiles, either(1, "a"))); static assert(!__traits(compiles, either(1.0, "a"))); static assert(!__traits(compiles, either('a', "a")));
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