toTree.js

var toTree = function(comments) {
    comments.sort(function(x, y) {return -(x.degree-y.degree)}) //Sorts by degree, descending.
    var treeDegree = comments[0].degree; //Max degree
    var commentsByDegree = {};
    for(var comment of comments) {
        //Separates comments by degree.
        comment.comments = [];
        if(commentsByDegree.hasOwnProperty(comment.degree)) {
            commentsByDegree[comment.degree].push(comment);
        }
        else {
            commentsByDegree[comment.degree] = [comment];
        }
    }
    for(var i = treeDegree-1; i >=0; i--) {
        //For each degree, starting from the second last, all the way to zero
        for(var comment of commentsByDegree[i+1]) {
            //We look one by one at the comments in the higher degree
            for(var parentComment of commentsByDegree[i]) {
                //And if they have a 'parent' field in one of the comments
                if(comment.parent != parentComment._id) continue;
                //We add them as a child comment.
                parentComment.comments.push(comment)
            }
        }
    }
    //At the end, the array at degree zero contains the full comment tree.
    return commentsByDegree[0];
}