<%= form_for @user, :html => {:multipart => true} do |f| %>
<p>
<label>My Avatar</label>
<%= f.file_field :avatar %>
<%= f.hidden_field :avatar_cache %> # сохраняет изображения если форма не валидна
</p>
<% end %>a = [{"2014-05-31" => 3}, {"2014-06-01" => 5}]
b = [{"2014-05-29" => 0}, {"2014-05-30" => 0}, {"2014-05-31" => 0}, {"2014-06-01" => 0}, {"2014-06-02" => 0}]
a.each {|c| b.select {|s| s.keys.first == c.keys.first}.first[c.keys.first] = c.values.first}