stats: fix O(n^2) performance, now much faster on large journals

hledger/Hledger/Cli/Stats.hs

@@ -13,6 +13,8 @@ where
 import Data.List
 import Data.Maybe
 import Data.Ord
+import Data.HashSet (size, fromList)
+import Data.Text (pack)
 import Data.Time.Calendar
 import System.Console.CmdArgs.Explicit
 import Text.Printf
@@ -63,7 +65,7 @@ showLedgerStats l today span =
         ,("Transactions", printf "%d (%0.1f per day)" tnum txnrate)
         ,("Transactions last 30 days", printf "%d (%0.1f per day)" tnum30 txnrate30)
         ,("Transactions last 7 days", printf "%d (%0.1f per day)" tnum7 txnrate7)
-        ,("Payees/descriptions", show $ length $ nub $ map tdescription ts)
+        ,("Payees/descriptions", show $ size $ fromList $ map (pack . tdescription) ts)
         ,("Accounts", printf "%d (depth %d)" acctnum acctdepth)
         ,("Commodities", printf "%s (%s)" (show $ length cs) (intercalate ", " cs))
       -- Transactions this month     : %(monthtxns)s (last month in the same period: %(lastmonthtxns)s)

hledger/hledger.cabal

@@ -74,6 +74,7 @@ library
                  ,base-compat >= 0.8.1
                  -- ,cabal-file-th
                  ,containers
+                 ,unordered-containers
                  ,cmdargs >= 0.10 && < 0.11
                  ,csv
                  -- ,data-pprint >= 0.2.1 && < 0.3
@@ -128,6 +129,7 @@ executable hledger
                  ,base >= 4.3 && < 5
                  ,base-compat >= 0.8.1
                  ,containers
+                 ,unordered-containers
                  ,cmdargs >= 0.10 && < 0.11
                  ,csv
                  -- ,data-pprint >= 0.2.1 && < 0.3