storing _data in an array

[allergeek]

Hi,
my blog runs on Harp and I'd love to have a list of posts. The post content is grouped into themes though, for example:

/post
/nutrition
post-title.jade
/running
post-title.jade
...

I followed an example found at http://harpjs.com/recipes/blog-posts-list
– and it works well with a variable holding a single value, but not with an array.

Do you think this is possible to accomplish?
Thank you!

postsEN = [];
groot = [];
groot = ["public.post.nutrition._data","public.post.neuroscience._data"];
for (var post in groot) {
  postsEN.push(groot[post].title);
};