Get top N items per group in Ruby on Rails -


i have model fields "date" , "frequency" (frequency integer). i'm trying top 5 frequencies per date. want group date, top 5 per group.

what have far retrieves top 1 in group:

observation.channel("channelone").order('date', 'frequency desc').group(:date).having('frequency = max(frequency)')

i want max(frequency) plus second, third, fourth , fifth largest per date.

sorry if simple or if terminology off; i've started rails :)

you can use this:

 observation    .select("obs1.*")    .from("observations obs1")    .joins("left join observations obs2 on obs1.date = obs2.date , obs1.frequency <= obs2.frequency")    .group("obs1.date, obs1.id")    .having("count(*) <= 5")    .order("obs1.date, obs2.frequency")

this query returns top 5 frequencies each date.


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