Linq GroupBy. Return top one item of a subset of data

Question

I have a table of flight price data and I want to return the top 1 cheapest flight to each destination destination. The table has the following basic fields:

FlightInfoID
AirportFrom
AirportTo
Price

I tried the following but it did not return the results I expected as there were multiple items for a specific destination and I only want 1 result per destination so if I have 50 destinations I would get 50 items returned.

lstBestFlightDealsForAllRoutes.OrderBy(p=> p.Price).GroupBy(x => x.AirportTo).First();

switch the groupby and orderby. – Dustin Kingen Mar 11 '13 at 15:14 — Dustin Kingen, Mar 11 '13 at 15:14

score 7 · Accepted Answer · answered Mar 11 '13 at 15:14

7

from f in lstBestFlightDealsForAllRoutes
group f by new { f.AirportFrom, f.AirportTo } into g // group by route
select g.OrderBy(x => x.Price).First() // select cheapest flight

answered Mar 11 '13 at 15:14

Sergey Berezovskiy

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score 4 · Answer 2 · answered Mar 11 '13 at 15:14

Group flights by destination
From each group select the cheapest flight in the group

Lniq makes 2 difficult (the Minimum function is useless), but you can do it (with a small performance cost) by ordering each group by price and selecting the first from each group, eg.

flights.GroupBy(f => f.Destination).Select(g => g.OrderBy(f => f.Cost)).Select(g => g.First())

Linq GroupBy. Return top one item of a subset of data

2 Answers2