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Function `std.algorithm.searching.count`

The first version counts the number of elements x in r for which pred(x, value) is true. pred defaults to equality. Performs Ο(haystack.length) evaluations of pred.


						
				size_t count(alias pred, Range, E)
				(
				

				  Range haystack,
				

				  E needle
				

				)
				

				if (isInputRange!Range && !isInfinite!Range && is(typeof(binaryFun!pred(haystack.front, needle))));
				

				

				size_t count(alias pred, R1, R2)
				(
				

				  R1 haystack,
				

				  R2 needle
				

				)
				

				if (isForwardRange!R1 && !isInfinite!R1 && isForwardRange!R2 && is(typeof(binaryFun!pred(haystack.front, needle.front))));
				

				

				size_t count(alias pred, R)
				(
				

				  R haystack
				

				)
				

				if (isInputRange!R && !isInfinite!R && is(typeof(unaryFun!pred(haystack.front))));
				

				

				size_t count(R)
				(
				

				  R haystack
				

				)
				

				if (isInputRange!R && !isInfinite!R);

The second version returns the number of times needle occurs in haystack. Throws an exception if needle.empty, as the count of the empty range in any range would be infinite. Overlapped counts are not considered, for example count("aaa", "aa") is 1, not 2.

The third version counts the elements for which pred(x) is true. Performs Ο(haystack.length) evaluations of pred.

The fourth version counts the number of elements in a range. It is an optimization for the third version: if the given range has the length property the count is returned right away, otherwise performs Ο(haystack.length) to walk the range.

Note

Regardless of the overload, count will not accept infinite ranges for haystack.

Parameters

Name	Description
pred	The predicate to evaluate.
haystack	The range to count.
needle	The element or sub-range to count in the `haystack`.

Returns

The number of positions in the haystack for which pred returned true.

Example

import std.uni : toLower;

// count elements in range
int[] a = [ 1, 2, 4, 3, 2, 5, 3, 2, 4 ];
writeln(count(a)); // 9
writeln(count(a, 2)); // 3
writeln(count!("a > b")(a, 2)); // 5
// count range in range
writeln(count("abcadfabf", "ab")); // 2
writeln(count("ababab", "abab")); // 1
writeln(count("ababab", "abx")); // 0
// fuzzy count range in range
writeln(count!((a, b) => toLower(a) == toLower(b))("AbcAdFaBf", "ab")); // 2
// count predicate in range
writeln(count!("a > 1")(a)); // 8

Authors

Andrei Alexandrescu

License

Boost License 1.0.