Idiomatic adjacent_difference

[John Colvin via Digitalmars-d-learn]

On Friday, 16 October 2015 at 11:11:28 UTC, Guillaume Chatelet 
wrote:
> Is there an idiomatic way to do:
>
> int[] numbers = [0, 1, 2, 3];
> assert(adjacent_diff(numbers) == [1, 1, 1]);
>
> I can't find something useful in the std library.

import std.range, std.algorithm;

auto slidingWindow(R)(R r, size_t n)
if(isForwardRange!R)
{
	//you could definitely do this with less overhead
	return roundRobin(r.chunks(n), r.save.drop(1).chunks(n))
		.filter!(p => p.length == n);
}

auto adjacentDiff(R)(R r)
{
	return r.slidingWindow(2).map!"a[1] - a[0]";
}

unittest
{
	import std.stdio;
	int[] numbers = [0, 1, 2, 3];
	writeln(numbers.slidingWindow(2));
	writeln(adjacentDiff(numbers));
	assert(adjacentDiff(numbers).equal([1, 1, 1]));
}