Use dynamic modulo to incrementally splice an array.

modulo-splice.php

<?php

    /**
     * Provided a threshold, determine modulo to keep every m-th item in the
     * array where m = ceil(count($array) / $threshold)
     *
     * @param $arr
     * @param $threshold
     * @param string $round
     * @param bool $keepLastOverFirst
     * @return array
     * @throws InvalidArgumentException
     */
    public static function moduloSpliceArray(array $arr, $threshold, $round = 'ceil', $keepLastOverFirst = false)
    {
        $round_funcs = ['ceil', 'floor', 'round'];
        $reduce_func = $keepLastOverFirst ? 'array_pop' : 'array_shift';
        $acc_func = $keepLastOverFirst ? 'array_unshift' : 'array_push';

        $count = count($arr);
        if ($count <= $threshold) {
            return $arr;
        }

        if (! in_array($round, $round_funcs)) {
            throw new InvalidArgumentException('The $round argument should be '.implode(',', $round_funcs));
        }

        $modulo = $round(floatval($count) / $threshold);

        $arr_modulo = [];
        $counter = 0;
        if ($modulo > 1) {
            while ($item = $reduce_func($arr)) {
                if (! $counter || $counter % $modulo == 0) {
                    $acc_func($arr_modulo, $item);
                }
                $counter++;
            }
        }

        return $arr_modulo;
    }