Active admin numeric range / number range filter

active_admin.scss

form.filter_form .filter_form_field.filter_numeric_range input[type='text'] {
  background-position: 100% 3px;
  background-repeat: no-repeat;
  padding-right: 25px;
  width: calc(50% - 3px);
}

form.filter_form .filter_form_field.filter_numeric_range .separator, form.filter_form .filter_form_field.filter_numeric_range input[type='text'] {
  display: inline-block;
  float: none;
}

filter_numeric_range_input.rb

module ActiveAdmin
  module Inputs
    module Filters
      class NumericRangeInput < ::Formtastic::Inputs::StringInput
        include Base

        def to_html
          input_wrapping do
            [ label_html,
              builder.text_field(gt_input_name, input_html_options(gt_input_name, gt_input_placeholder)),
              builder.text_field(lt_input_name, input_html_options(lt_input_name, lt_input_placeholder)),
            ].join("\n").html_safe
          end
        end

        def gt_input_name
          "#{method}_gteq"
        end
        alias :input_name :gt_input_name

        def lt_input_name
          "#{method}_lteq"
        end

        def input_html_options(input_name = gt_input_name, placeholder = gt_input_placeholder)
          current_value = @object.public_send(input_name)
          { size: 12, placeholder: placeholder, value: current_value }
        end

        def gt_input_placeholder
          I18n.t('active_admin.filters.predicates.from')
        end

        def lt_input_placeholder
          I18n.t('active_admin.filters.predicates.to')
        end
      end
    end
  end
end