//Add class in articles depending span
$(".blog-1 .category a").each(function() {
  category = $(this).text();
  $(this).parents(".blog-1").addClass(category);
})

//Filter options
$("#list-of-categories").change(function () {
  var value = $( "option:selected" ).text();
  $('.blog-1').show().filter(':not(.' + value + ')').hide();
});