<?php
/*
span :: (a -> Bool) -> [a] -> ([a],[a])
span _ xs@[] = (xs, xs)
span p xs@(x:xs')
| p x = let (ys,zs) = span p xs' in (x:ys,zs)
| otherwise = ([],xs)
*/
function span($p, $xs) {
if (empty($xs)) {
return [[], []];
}
$xs_ = $xs;
$x = array_shift($xs_);
if ($p($x)) {
list($ys, $zs) = span($p, $xs_);
return [array_merge([$x], $ys), $zs];
}
return [[], $xs];
}
/*
groupBy :: (a -> a -> Bool) -> [a] -> [[a]]
groupBy _ [] = []
groupBy eq (x:xs) = (x:ys) : groupBy eq zs
where (ys,zs) = span (eq x) xs
*/
function array_group(callable $eq, array $xs) {
if (empty($xs)) {
return [];
}
$x = array_shift($xs);
// curry of $eq
$eqx = function ($y) use ($eq, $x) { return $eq($x, $y); };
list($ys, $zs) = span($eqx, $xs);
return array_merge([array_merge([$x], $ys)], array_group($eq, $zs));
}
function it($m,$p){echo ($p?'OK':'NO')." It $m\n"; if(!$p){$GLOBALS['f']=1;}}
function done(){if(@$GLOBALS['f'])die(1);}
it('spans elements which match', span(function ($x) { return $x < 3; }, [1, 2, 3]) === [[1, 2], [3]]);
it('spans elements which match from the start', span(function ($x) { return $x == 3; }, [1, 6, 3, 3]) === [[], [1, 2, 3, 3]]);
it('spans returns empty lists on empty list', span(function ($x) { return false; }, []) === [[], []]);
it('groups elements recursively', array_group(function ($a, $b) { return $a <= ($b-1); }, [1, 1, 2, 1]) === [[1, 1], [2], [1]]);
print_r(array_group(function ($a, $b) { return $a <= ($b-1); }, [1, 1, 2, 1]) === [[1, 1], [2], [1]]);
preferences:
43.35 ms | 402 KiB | 5 Q