Filter posts in Jekyll

[csbartus]

Ahoy,

I'm trying to filter posts with Jekyll. Something like:

{% for work in site.categories.works year: 2011 %}

which would fetch posts from 2011.
I've added a new filter in "_plugins/liquid_extensions.rb" but it is
totally ignored.

module YearFilter
def year(input, year)
[]
end
end
Liquid::Template.register_filter(YearFilter)

Any help would be very appreciated. Thanks!