To remove duplicates and keep order

[dlangBugzillaToGithub]

bearophile_hugs reported this on 2013-05-21T16:59:50Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=10131

CC List

• greensunny12
• razvan.nitu1305

Description

I suggest to add to Phobos a function with semantics similar to this one, that sometimes I find useful:


T[] noDupes(T)(in T[] s) {
    import std.algorithm: canFind;
    T[] result;
    foreach (T c; s)
        if (!result.canFind(c))
            result ~= c;
    return result;
}

void main() {
    import std.string: squeeze;
    assert("AAAA".noDupes == "A");
    assert("AAAA".squeeze == "A");
    assert("ABAC".noDupes == "ABC");
    assert("ABAC".squeeze == "ABAC");
}


Notes:
- It's related to std.string.squeeze and std.algorithm.uniq, but they need the items to be sorted to remove all the duplicates, while the function discussed here doesn't change the order of the items.
- The implementation shown here is slow, O(n^2), because it's meant to just show the semantics clearly. If the items are hashable it's possible to create a O(n) implementation, storing the items in a hash. If the items are comparable it's possible to write a O(n ln n) version that creates an array of sorted pointers and then performs binary searches on it. The O(n^2) version is a fallback if the items are not hashable nor comparable. The three versions are meant to be three parts of the same general function.

[dlangBugzillaToGithub]

greensunny12 commented on 2017-10-10T13:15:12Z

PR https://github.com/dlang/phobos/pull/5774