reddit comment sorting algorithm implemented for habr

habra-reddit-sort.js

// License=WTFPLv2
$(function () {
    function sortCommentList(parent, recursive) {
        var comments = $(parent).find('>.comment_item');
        $(parent).append(keySort(comments, extractRating, true));
        recursive && comments.find('>.reply_comments:has(div)').each(function (idx, replies) {
            sortCommentList(replies, recursive);
        });
    }

    function extractRating(comment) {
        try {
            var title = $(comment).find('>.comment_body .score').attr('title'),
                mat = /↑(\d+).*?↓(\d+)/.exec('' + title);
            return mat ? rating(+mat[1], +mat[2]) : 0;
        } catch (e) {
            return 0;
        }
    }

    function ratingQ(max, z, cnt, total) {
        if (!(max > 0 && z > 0 && cnt >= 0 && total >= 0)) {
            return 0;
        }
        if (cnt === 0) {
            return 0;
        }
        var t = 2 * (total / max) / (z * z),
            ph = (total / max) / cnt;
        return max * (t * ph + 1 - Math.sqrt(2 * t * ph * (1 - ph) + 1)) / (t + 2);
    }

    function rating(pos, neg) {
        return ratingQ(1, 1.6, (pos + neg), pos);
    }

    function keySort(arr, keyFn, reverse) {
        return arr.slice().sort(function (a, b) {
            var ka = keyFn(a),
                kb = keyFn(b);
            return ka === kb ? 0 : (ka > kb) ^ !reverse ? 1 : -1;
        });
    }
    
    sortCommentList($('#comments'), true);
});