## id만 남기고 인덱스 추출 ### map ``` index = User.all.order(engagement: :desc).map(&:id).index(current_user.id) ``` ### pluck Use pluck as a shortcut to select one or more attributes without loading a bunch of records just to grab the attributes you want. ``` ids = User.order(engagement: :desc).pluck(:id) # => [ 1, 2, 3, ... ] index = ids.index(current_user.id) ``` ### 선택적 결과 값 ``` Location.select(:name, :website, :city).find(row.id) ``` ## 레퍼런스 + ActiveRecord find position(index) of record. (https://goo.gl/QDeXaf) + ActiveRecord find and only return selected columns (https://goo.gl/qmDvFw)