Re: [Haskell-cafe] Multi groupby with foldl' and Map.insertWithKey

On Wed, Dec 28, 2016 at 9:28 AM, Cody Goodman

wrote:

My goal is to take data like this:

[ Info 0 "Alcohol" "TX" , Info 1 "Alcohol" "TX" , Info 2 "Pregnancy" "MA" ]

and build a Map like this:

[("MA",[("Pregnancy",1)]),("TX",[("Alcohol",2)])]

You can convert each individual record to a singleton map: wrapRecord :: Info -> M.Map String (M.Map String Integer) wrapRecord (Info _ state healthTopic) = M.singleton state (M.singleton healthTopic 1) and then union all these singletons: numTopicsPerState = M.unionsWith (M.unionWith (+)) . map wrapRecord $ [Info 0 "Alcohol" "TX", Info 1 "Alcohol" "TX", Info 2 "Pregnancy" "MA"]