@category1 = @posts.where(category: "1")
@category2 = @posts.where(category: "2")
@category3 = @posts.where(category: "3")

{ title: "Category 1",       value:  22,   color: "#2C3E50" },
{ title: "Category 2",       value:  80,   color: "#FC4349" },
{ title: "Category 3",       value:  70,   color: "#6DBCDB" },

<div id="metrics" data-category1="<%= @category1.size %>">
</div>

var $category1 = $("#metrics").data("category1")

@category1 = @posts.where(category: "1")
gon.category1Size = @category1.size

alert(gon.category1Size);

{ title: "Category 1",       value:  22,   color: "#2C3E50" },
{ title: "Category 2",       value:  80,   color: "#FC4349" },
{ title: "Category 3",       value:  70,   color: "#6DBCDB" },