std.range.rotate?

[dlangBugzillaToGithub]

bearophile_hugs reported this on 2013-08-03T13:09:02Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=10754

CC List

• crazymonkyyy

Description

std.algorithm.bringToFront is efficient to rotate arrays in-place, but often in range-based coding (in UFCS chains) I'd like a lazy range that yields the rotated items and doesn't modify the order of the items of the original data. So in Phobos I'd like a lazy range with a semantics similar to this:

import std.stdio, std.range;

auto rotate(R)(R r, in int n) pure nothrow
if (isRandomAccessRange!R) {
    immutable int len = r.walkLength;
    return r.cycle.drop(n >= 0 ? n : len + n).take(len);
}

void main() {
    foreach (shift; -5 .. 5)
        [10, 20, 30, 40, 50].rotate(shift).writeln;
}


To work like this the input array should be a random access one. (You can write a rotate() for a bidirectional array, but I think there is less need for it).

[dlangBugzillaToGithub]

crazymonkyyy commented on 2022-09-10T15:44:48Z

I also dislike the wonky bringToFront; tho I think it should be in place 

my take:
```d
void rotate(T)(T foo,int i){
	auto bar=foo.cycle.drop(i).take(foo.length).array[];
	foreach(ref e;foo){
		e=bar.front;
		bar.popFront;
}}
unittest{
	auto foo=[1,2,3,4,5];
	foo.rotate(2);
	foo.writeln;
}
```