Bug 13940 – std.algorithm.argMin

I've often needed this function (and added it really early on to my utilities library) auto argMin(alias f, alias pred = "a < b", InputRange)(InputRange arg) { assert(!arg.empty); return arg.minPos!((a, b) => binaryFun!pred(f(a), f(b))).front; } Ideally the implementation would cache the evaluation of f(x) so that it is only evaluated once per element. http://en.wikipedia.org/wiki/Arg_max

See Issue 4705 where I suggested to add to max/min an optional "key" argument unary function. So to find the min or max with a key of a sequence you use a reduce: someRange.reduce!(max!abs) It evaluates the key function only once for item. It's similar to the max/min Python functions. And it's probably among my top additions to Phobos, beside a pairwise (Issue 6788 ).

(In reply to bearophile_hugs from comment #1) > See Issue 4705 where I suggested to add to max/min an optional "key" > argument unary function. > > So to find the min or max with a key of a sequence you use a reduce: > > someRange.reduce!(max!abs) > > It evaluates the key function only once for item. In the reduce, the max!abs would be called n - 1 times, and each call to max!abs(a, b) would involve two calls to abs, so 2(n - 1) calls total, not n (unless I've misunderstood somewhere).

(In reply to Peter Alexander from comment #2) > In the reduce, the max!abs would be called n - 1 times, and each call to > max!abs(a, b) would involve two calls to abs, so 2(n - 1) calls total, not n > (unless I've misunderstood somewhere). Thank you for your answer (that should go also in Issue 4705 ). If you are right, then: - I want both functions for "min with key" and "max with key" (putting only one of them in Phobos sucks); - I prefer an unary function instead of a binary function. When you get used to unary functions they are much more handy. So I guess you can call call them keyMax and keyMin.

So its usage looks like: someRange.keyMin!abs someRange.keyMax!abs

See also the maxBy and minBy of F#: http://msdn.microsoft.com/en-us/library/ee340421.aspx http://msdn.microsoft.com/en-us/library/ee340252.aspx

Min and maxElement are part of Phobos since 2.071 - the crowd goes wild :) They support a custom mapping function and evaluation of the mapping is only done once.