-----------------------------
place  | key        | weights
----------------------------
amazon | lion       | [ 34, 23, 56 ]
north  | bear       | [ 90, 45]
amazon | lion       | [ 38, 30, 50 ]
amazon | bear       | [ 45 ]
amazon | bear       | [ 40 ]

-----------------------------
place  | key        | average
----------------------------
amazon | lion1      | 36.0      #(34 + 38)/2
amazon | lion2      | 26.5      #(23 + 30)/2
amazon | lion3      | 53.0      #(50 + 56)/2
north  | bear1      | 90        #(90)/1
north  | bear2      | 45        #(45)/1
amazon | bear1      | 42.5      #(45 + 40)/2