Counties and Conduit

Posted on July 26, 2015

About two years ago, I worked with my grandpa to produce a database of cities (at the latitude and longitude level) and historic counties / state based on GIS files with polygons from Newberry. It wasn’t too difficult, I loaded them into PostGIS on a local PostgreSQL instance, joined based on cities being inside a polygon or not, where each polygon had an associated historic county name, state, territory, and date range.

The problem I solved for my grandpa was determining where genealogy records may reside at given locations for periods of time. For example: Joe Jones died in 1890 in Overbrook, New Jersey. Today the county is Camden, but that may not have been the county in 1830, which is Gloucester. With this information, a genealogist can find out that they should look next at the Gloucester records.

At first, I worked on only one US state of information, to see if my query worked properly. It wasn’t a simple query to execute, the timing it took felt higher than \(O(N*M)\), but then again both \(N\) and \(M\) were significant in size.

insert into cities values ( 'Alabama' , 'Baldwin' , 'Atkins Mill' , ST_GeomFromText( 'POINT(-87.86333 32.98389)' , 26768 )); insert into cities values ( 'Alabama' , 'Baldwin' , 'Barlow Landing' , ST_GeomFromText( 'POINT(-87.8725 30.95722)' , 26768 )); ...

Unfortunately, I cannot find the original query I used on the joined data.

After producing this information, two years ago, there were a few duplicates. I underestimated just how much.

My Grandfather published one book on his current home state with the information after trudging through all the duplicates and messy details. But now that the one state is finished, it is time to optimize the process.

Here’s one example from Kansas, Oursler.

State, County, City, Historic State, Historic County, Start Date, End Date, lat, long ... "Kansas" , "Marion" , "Oursler" ,, "Unorganized Federal Territory" , 5 / 6 / 1828 0 : 00 : 00 , 6 / 27 / 1834 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" ,, "Missouri Territory" , 2 / 22 / 1819 0 : 00 : 00 , 8 / 9 / 1821 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "MO" , "Non-County Area 1" , 7 / 4 / 1819 0 : 00 : 00 , 12 / 31 / 1820 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" ,, "Unorganized Federal Territory" , 8 / 10 / 1821 0 : 00 : 00 , 12 / 12 / 1850 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "MO" , "ST. LOUIS (Mo.)" , 10 / 1 / 1804 0 : 00 : 00 , 12 / 6 / 1812 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" ,, "Unorganized Federal Territory" , 5 / 26 / 1824 0 : 00 : 00 , 5 / 5 / 1828 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" ,, "Unorganized Federal Territory" , 8 / 10 / 1821 0 : 00 : 00 , 5 / 25 / 1824 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "MO" , "Non-County Area 1" , 1 / 1 / 1821 0 : 00 : 00 , 8 / 9 / 1821 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" ,, "Unorganized Federal Territory" , 6 / 28 / 1834 0 : 00 : 00 , 3 / 27 / 1837 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "KS" , "MARION" , 8 / 25 / 1855 0 : 00 : 00 , 2 / 16 / 1860 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "MO" , "ST. LOUIS (Mo.)" , 10 / 1 / 1804 0 : 00 : 00 , 12 / 6 / 1812 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "KS" , "MARION" , 3 / 6 / 1873 0 : 00 : 00 , 12 / 31 / 2000 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "KS" , "MARION" , 2 / 22 / 1865 0 : 00 : 00 , 2 / 25 / 1867 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "MO" , "St. Louis District" , 10 / 1 / 1804 0 : 00 : 00 , 12 / 6 / 1812 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "KS" , "MARION" , 2 / 26 / 1867 0 : 00 : 00 , 3 / 2 / 1868 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "MO" , "ST. LOUIS (Mo.)" , 10 / 1 / 1804 0 : 00 : 00 , 12 / 6 / 1812 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" ,, "Unorganized Federal Territory" , 12 / 13 / 1850 0 : 00 : 00 , 5 / 29 / 1854 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "KS" , "MARION" , 2 / 17 / 1860 0 : 00 : 00 , 2 / 21 / 1865 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "MO" , "ST. LOUIS (Mo.)" , 10 / 1 / 1804 0 : 00 : 00 , 12 / 6 / 1812 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "MO" , "ST. LOUIS (Mo.)" , 10 / 1 / 1804 0 : 00 : 00 , 12 / 6 / 1812 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "KS" , "MARION" , 3 / 3 / 1868 0 : 00 : 00 , 3 / 5 / 1873 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "KS" , "Kansas Territory" , 5 / 30 / 1854 0 : 00 : 00 , 8 / 24 / 1855 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "MO" , "Non-County Area 1" , 12 / 7 / 1812 0 : 00 : 00 , 12 / 30 / 1813 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "MO" , "Non-County Area 1" , 6 / 1 / 1819 0 : 00 : 00 , 7 / 3 / 1819 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "MO" , "Non-County Area 1" , 12 / 31 / 1813 0 : 00 : 00 , 2 / 21 / 1819 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" ,, "Missouri Territory" , 12 / 7 / 1812 0 : 00 : 00 , 2 / 21 / 1819 0 : 00 : 00 , 38.29 ,- 96.98 "Kansas" , "Marion" , "Oursler" , "MO" , "Non-County Area 1" , 2 / 22 / 1819 0 : 00 : 00 , 5 / 31 / 1819 0 : 00 : 00 , 38.29 ,- 96.98

As you can see, the details that came back from my grandpa’s Microsoft Access export are not necessarily in a convenient order. Nor are the dates lexicographically friendly for sorting.

This was my starting point in this chapter of the project.

Starting point

First, I needed to come up with a sensible representation. Having everything represented perfectly in Haskell wasn’t my goal. I just needed to do some basic grouping, sorting, and event-sourcing.

My first decision on the data structure was, ByteString is fine for everything, so long as they were lexicographically sort-friendly.

I also had no interest in using a complicated csv-conduit package where I had doubts of it being stream-frienly on a row basis. So I wrote my own CSV parser of sorts. It isn’t perfect, but it works on the data I need.

quote :: Word8 quote = BI.c2w '\"' comma :: Word8 comma = BI.c2w ',' csvSplit :: ( Monad m) => Conduit B.ByteString m [ B.ByteString ] csvSplit = do v <- await case v of Nothing -> return () Just v' -> do yield $ split v' csvSplit where split v | B.null v = [] | B.head v == comma = B.empty : split (B.drop 1 v) | B.head v == quote = let str = B.drop 1 v (quoted,rest) = B.break ( == quote) str requoted = B.cons quote $ B.snoc quoted quote in requoted : split (B.drop 2 rest) | otherwise = let (part,rest) = B.break ( == comma) v in part : split (B.drop 1 rest)

Awesome, now I have a list of bytestrings (for each field). Let’s double check that this parses the right amount of fields for the entire file.

import qualified Data.Conduit as C import qualified Data.Conduit.Binary as CB import qualified Control.Monad.Trans.Resource as R -- Conduit combinators WOULD NOT WORK in ghci (it can't find it..?) -- So, I used my own helpers instead (printC) printC :: ( Show a, MonadIO m) => C.Sink a m () printC = do v <- C.await case v of Just v' -> do liftIO . putStrLn . show $ v' printC Nothing -> return () listCount :: ( Monad m) => C.Conduit [a] m Int listCount = do v <- C.await case v of Nothing -> return () Just v' -> do C.yield $ length v' listCount equalLength :: ( Monad m, Eq a) => C.Conduit a m (a, Int ) equalLength = el Nothing 0 where el ov c = do v <- C.await case (ov,v) of ( Nothing , Nothing ) -> return () ( Just x, Nothing ) -> C.yield (x, c) ( Nothing , Just _) -> el v 1 ( Just x1, Just x2) -> if x1 == x2 then el ov (c + 1 ) else do C.yield (x1,c) el v 1 main = do R.runResourceT $ CB.sourceFile "USA Base Unlinked.txt" $= CB.lines $= E.csvSplit $= listCount $= equalLength $$ printC

And out came something like (9,400000)

Good! Now I can move on to putting into my internal representation and mess around with it.

Simple Data Structure

As I said above, ByteStrings would be good enough for me, though I’ll need to convert this messy date 10/1/1804 0:00:00 to something like 1804-10-01 .

data CountyRow = CountyRow { state :: B.ByteString , city :: B.ByteString , county :: B.ByteString , coordLat :: B.ByteString , coordLong :: B.ByteString , startDate :: B.ByteString , endDate :: B.ByteString , historicState :: B.ByteString , historicCounty :: B.ByteString } deriving ( Eq , Show ) convertOld :: [ B.ByteString ] -> CountyRow convertOld bs = CountyRow { state = s, city = ci, county = co, coordLat = cla , coordLong = clo, startDate = sd, endDate = ed , historicState = hs, historicCounty = hc } where s = bs !! 0 ci = bs !! 2 co = bs !! 1 cla = bs !! 7 clo = bs !! 8 sd = todate $ bs !! 5 ed = todate $ bs !! 6 hc = bs !! 4 hs = bs !! 3 -- I have the Word8 things in my 'Extras' module qualified by E. -- ByteString Internals has a nice Char to Word8 fn for stuff like this space :: Word8 space = BI.c2w ' ' slash :: Word8 slash = BI.c2w '/' dash :: Word8 dash = BI.c2w '-' zero :: Word8 zero = BI.c2w '0' todate :: B.ByteString -> B.ByteString todate b = let (date, _) = B.break ( == E.space) b parts = B.split E.slash date year = parts !! 2 month = parts !! 0 day = parts !! 1 arrange = [ year , if B.length month < 2 then B.cons E.zero month else month , if B.length day < 2 then B.cons E.zero day else day ] redash = intersperse (B.singleton E.dash) arrange in B.concat redash

Now that I have my parsing code set up, I can do something like this to print it out and see if it came out right.

import qualified Data.Conduit.Binary as CB import qualified Data.Conduit.List as CL import qualified Control.Monad.Trans.Resource as R main = do R.runResourceT $ CB.sourceFile "USA Base Unlinked.txt" $= CB.lines $= E.csvSplit $= CL.map convertOld $$ printC

And indeed I got a nice representation out!

Reordering the data

However, because the data is partially sorted, and I know it is partially sorted, I can pause and reorder the stream so each row is friendly for doing some quasi-event sourcing.

At first I wrote the code specific to a a given sorting and comparison, but I found Conduit amazing at refactoring and generalization.

collect :: ( Monad m) => (a -> a -> Bool ) -> Conduit a m [a] collect f = c Nothing [] where c ov s = do v <- await case (ov, v) of ( Nothing , Nothing ) -> return () ( Just _, Nothing ) -> yield s ( Nothing , Just x) -> c v [x] ( Just x1, Just x2) -> if f x1 x2 then c ov (x2 : s) else do yield s c v [x2] implode :: ( Monad m) => Conduit [a] m a implode = do v <- await case v of Nothing -> return () Just v' -> do M.mapM yield v' implode collectAndSort :: ( Monad m) => (a -> a -> Bool ) -> (a -> a -> Ordering ) -> Conduit a m a collectAndSort f c = collect f $= CL.map (sortBy c) $= implode cityKey :: CountyRow -> [ B.ByteString ] cityKey cr = [ state cr , city cr , coordLat cr , coordLong cr ] compareNormal :: CountyRow -> CountyRow -> Ordering compareNormal c1 c2 | state c1 < state c2 = LT | state c1 > state c1 = GT | city c1 < city c2 = LT | city c1 > city c2 = GT | county c1 < county c2 = LT | county c1 > county c2 = GT | coordLat c1 < coordLat c2 = LT | coordLat c1 > coordLat c2 = GT | coordLong c1 < coordLong c2 = LT | coordLong c1 > coordLong c2 = GT | startDate c1 < startDate c2 = LT | startDate c1 > startDate c2 = GT | endDate c1 < endDate c2 = LT | endDate c1 > endDate c2 = GT | historicState c1 < historicState c2 = LT | historicState c1 > historicState c2 = GT | historicCounty c1 < historicCounty c2 = LT | historicCounty c1 > historicCounty c2 = GT | otherwise = EQ

Now, I can use something like $= collectAndSort sameCity compareNormal to reorder the stream into a manner convenient for processing.

Merging

With the data in an event sourcing friendly format, I can have a somewhat stateful conduit (via tail call recursion) to merge information.

Again, I found Conduit amazingly friendly for refactoring and generalization. The concept of merging mostly needs to answer “Is it mergeable?” and “How do to merge?”

merge :: ( Monad m) => (a -> a -> Bool ) -> (a -> a -> a) -> Conduit a m a merge comp f = m Nothing where m ov = do v <- await case (ov, v) of ( Nothing , Nothing ) -> return () ( Just x, Nothing ) -> yield x ( Nothing , Just x) -> m v ( Just x1, Just x2) -> do if comp x1 x2 then m $ Just $ f x1 x2 else yield x1 >> m v mergeId :: ( Monad m, Eq a) => Conduit a m a mergeId = merge ( == ) (\v _ -> v) historyKey :: CountyRow -> [ B.ByteString ] historyKey cr = [ historicCounty cr , historicState cr ] mergeCounties :: ( Monad m) => C.Conduit CountyRow m CountyRow mergeCounties = E.merge (\x1 x2 -> historyKey x1 == historyKey x2) (\x1 x2 -> let end = max (endDate x1) (endDate x2) start = min (startDate x1) (startDate x2) in x2 {startDate = start, endDate = end})

Turns out that the data I had was adequately sorted, but not the best, since city names weren’t in perfect order. Luckily, Conduit being generalization friendly made it so I could reorder the entire state before processing! Though this added some time and memory to processing.

So I started making my own sorted version.

convert :: [ B.ByteString ] -> CountyRow convert bs = CountyRow { state = bs !! 0 , city = bs !! 1 , county = bs !! 2 , coordLat = bs !! 3 , coordLong = bs !! 4 , startDate = bs !! 5 , endDate = bs !! 6 , historicState = bs !! 7 , historicCounty = bs !! 8 } sameState :: CountyRow -> CountyRow -> Bool sameState r1 r2 = state r1 == state r2 oldSrc :: ( MonadIO m, R.MonadResource m) => C.Source m CountyRow oldSrc = countiesOld $= convertingOld $= collectState where countiesOld = CB.sourceFile "USA Base Unlinked.txt" $= CB.lines convertingOld = E.csvSplit $= CL.map convertOld collectState = E.collectAndSort sameState compareNormal newSrc :: ( MonadIO m, R.MonadResource m) => C.Source m CountyRow newSrc = counties $= converting where counties = CB.sourceFile "Ordered USA.csv" $= CB.lines converting = E.csvSplit $= CL.map convert toCSV = CL.map (B.concat . intersperse (B.singleton E.comma) . unconvert) withLines = CL.map (\v -> B.append v "

" ) sameCity :: CountyRow -> CountyRow -> Bool sameCity r1 r2 = cityKey r1 == cityKey r2 main1 = do R.runResourceT $ oldSrc $ E.collectAndSort sameCity compareNormal $= toCSV $= withLines $$ CB.sinkFile "Ordered USA.csv" main2 = do R.runResourceT $ newSrc -- Remove line duplicates $= E.mergeId -- Merge counties, keeping earliest and latest -- start and end dates respectively $= mergeCounties $= toCSV $= withLines $$ CB.sinkFile "Merged USA.csv"

So! Given that I first order things appropriately, now Oursler looks like

"Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1804-10-01 , 1812-12-06 , "MO" , "ST. LOUIS (Mo.)" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1804-10-01 , 1812-12-06 , "MO" , "ST. LOUIS (Mo.)" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1804-10-01 , 1812-12-06 , "MO" , "ST. LOUIS (Mo.)" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1804-10-01 , 1812-12-06 , "MO" , "ST. LOUIS (Mo.)" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1804-10-01 , 1812-12-06 , "MO" , "ST. LOUIS (Mo.)" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1804-10-01 , 1812-12-06 , "MO" , "St. Louis District" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1812-12-07 , 1813-12-30 , "MO" , "Non-County Area 1" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1812-12-07 , 1819-02-21 ,, "Missouri Territory" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1813-12-31 , 1819-02-21 , "MO" , "Non-County Area 1" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1819-02-22 , 1819-05-31 , "MO" , "Non-County Area 1" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1819-02-22 , 1821-08-09 ,, "Missouri Territory" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1819-06-01 , 1819-07-03 , "MO" , "Non-County Area 1" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1819-07-04 , 1820-12-31 , "MO" , "Non-County Area 1" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1821-01-01 , 1821-08-09 , "MO" , "Non-County Area 1" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1821-08-10 , 1824-05-25 ,, "Unorganized Federal Territory" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1821-08-10 , 1850-12-12 ,, "Unorganized Federal Territory" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1824-05-26 , 1828-05-05 ,, "Unorganized Federal Territory" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1828-05-06 , 1834-06-27 ,, "Unorganized Federal Territory" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1834-06-28 , 1837-03-27 ,, "Unorganized Federal Territory" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1850-12-13 , 1854-05-29 ,, "Unorganized Federal Territory" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1854-05-30 , 1855-08-24 , "KS" , "Kansas Territory" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1855-08-25 , 1860-02-16 , "KS" , "MARION" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1860-02-17 , 1865-02-21 , "KS" , "MARION" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1865-02-22 , 1867-02-25 , "KS" , "MARION" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1867-02-26 , 1868-03-02 , "KS" , "MARION" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1868-03-03 , 1873-03-05 , "KS" , "MARION" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1873-03-06 , 2000-12-31 , "KS" , "MARION"

Very neat! Now let’s see how it looks when I inspect the merged output.

"Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1804-10-01 , 1812-12-06 , "MO" , "ST. LOUIS (Mo.)" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1804-10-01 , 1812-12-06 , "MO" , "St. Louis District" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1812-12-07 , 1813-12-30 , "MO" , "Non-County Area 1" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1812-12-07 , 1819-02-21 ,, "Missouri Territory" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1813-12-31 , 1819-05-31 , "MO" , "Non-County Area 1" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1819-02-22 , 1821-08-09 ,, "Missouri Territory" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1819-06-01 , 1821-08-09 , "MO" , "Non-County Area 1" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1821-08-10 , 1854-05-29 ,, "Unorganized Federal Territory" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1854-05-30 , 1855-08-24 , "KS" , "Kansas Territory" "Kansas" , "Oursler" , "Marion" , 38.29 ,- 96.98 , 1855-08-25 , 2000-12-31 , "KS" , "MARION"

Oh yes!

This is what I wanted! Though there are some duplicates with the same dates, but different names. Since this is a domain decision, I’ll defer how to deal with that to my grandpa for now.

Conclusion

While working on this project, I recalled how Erlang passes state down for future messages. It may seem obvious in a functional programming world, but once it clicked here, it became very easy to handle how Conduit answers await .

Let’s review my merge function.

merge :: ( Monad m) => (a -> a -> Bool ) -> (a -> a -> a) -> Conduit a m a merge comp f = m Nothing where m ov = do v <- await case (ov, v) of ( Nothing , Nothing ) -> return () ( Just x, Nothing ) -> yield x ( Nothing , Just x) -> m v ( Just x1, Just x2) -> do if comp x1 x2 then m $ Just $ f x1 x2 else yield x1 >> m v

merge is really just a wrapper for a function m with an initial state. At the beginning of the stream (Nothing, Just x) -> m v , I just pass along what the recent value (wrapped in a Maybe ) is v . At the end of the stream (Just x, Nothing) -> yield x , I give up the value I have merged over time back to the stream. In the middle, (Just x1, Just x2) -> , I do the simple logic of merging or yielding the previous value when a merge is not appropriate.

I’m not sure how efficient this is from a stream fusion standpoint, though it handled my needs gracefully.

Also, notice how the functions comp and f are used, refactoring those out to be input functions required only 3 lines of change within merge , gave me an easy implementation to drop redundant stream inputs, and also have a domain specific mergeCounties Conduit with an understandable implementation.

Overall, I found the cognitive overhead of ‘Conduit’ to be amazingly light, followed the principle of least surprise, and solved my needs.

Although I made the decision of splitting stages into files due to the size and inequal weight of resorting at the state level, I could have easily just done something like

main3 = do R.runResourceT $ oldSrc $ E.collectAndSort sameCity compareNormal -- Remove line duplicates $= E.mergeId -- Merge counties, keeping earliest and latest -- start and end dates respectively $= mergeCounties $= toCSV $= withLines $$ CB.sinkFile "Merged USA.csv"

And it would just work.

Overall, I am very pleased with Snoyman’s work on Conduit.