market volume  numPurchases   transDate  avgDailyPurchases  AvgDailyPurchasesAll
JFK    500     32             20190102   50                 75
JFK    500     60             20190103   50                 75
ATL    450     40             20190102   40                 75

avgPercentCheaperThanAll
.22
.22
.75

weighted rating (WR) = (v ÷ (v+m)) × R + (m ÷ (v+m)) × C
v = volume of market
m = minimum volume required to be in the list
R = avgDailyPurchases
C = AvgDailyPurchasesAll