diff --git a/src/GEval/Core.hs b/src/GEval/Core.hs
index 474936e..4204931 100644
--- a/src/GEval/Core.hs
+++ b/src/GEval/Core.hs
@@ -34,8 +34,8 @@ module GEval.Core
       EvaluationContext(..),
       ParserSpec(..),
       fileAsLineSource,
-      checkAndGetFiles,
-      checkAndGetFilesSingleOut,
+      checkAndGetDataSource,
+      checkAndGetDataSources,
       checkMultipleOuts,
       checkMultipleOutsCore,
       gesMainMetric,
@@ -48,7 +48,8 @@ module GEval.Core
       FileProcessingOptions(..),
       readHeaderFileWrapper,
       getInHeader,
-      getOutHeader
+      getOutHeader,
+      addPreprocessing,
     ) where
 
 import Debug.Trace
@@ -266,22 +267,8 @@ data LineSource m = LineSource (ConduitT () Text m ()) (Text -> ItemTarget) (Tex
 
 geval :: GEvalSpecification -> IO [(SourceSpec, [MetricOutput])]
 geval gevalSpec = do
-  mInHeader <- readHeaderFileWrapper $ getInHeader gevalSpec
-  mOutHeader <- readHeaderFileWrapper $ getOutHeader gevalSpec
-  (inputSource, expectedSource, outSources) <- checkAndGetFiles False gevalSpec
-  let chDataSource = ChallengeDataSource {
-        challengeDataSourceInput = inputSource,
-        challengeDataSourceExpected = expectedSource,
-        challengeDataSourceSelector = gesSelector gevalSpec,
-        challengeDataSourcePreprocess = gesPreprocess gevalSpec,
-        challengeDataSourceFilter = Nothing,
-        challengeDataSourceInHeader = mInHeader,
-        challengeDataSourceOutHeader = mOutHeader }
-
-  results <- Prelude.mapM (\outSource -> gevalOnSingleOut gevalSpec
-                                                        DataSource {
-                             dataSourceChallengeData = chDataSource,
-                             dataSourceOut = outSource }) outSources
+  dataSources <- checkAndGetDataSources False gevalSpec
+  results <- Prelude.mapM (gevalOnSingleOut gevalSpec) dataSources
   return $ sortBy (\a b ->  (show $ fst a) `naturalComp` (show $ fst b)) results
 
 noGraph :: d -> Maybe GraphSeries
@@ -313,15 +300,15 @@ readHeaderFileWrapper (Just headerFilePath) = do
     Just header -> return $ Just header
     Nothing -> throwM $ NoHeaderFile headerFilePath
 
-checkAndGetFilesSingleOut :: Bool -> GEvalSpecification -> IO (SourceSpec, SourceSpec, SourceSpec)
-checkAndGetFilesSingleOut forceInput gevalSpec = do
-  res <- checkAndGetFiles forceInput gevalSpec
+checkAndGetDataSource :: Bool -> GEvalSpecification -> IO DataSource
+checkAndGetDataSource forceInput gevalSpec = do
+  res <- checkAndGetDataSources forceInput gevalSpec
   case res of
-    (inputSource, expectedSource, [outSource]) -> return (inputSource, expectedSource, outSource)
+    ([dataSource]) -> return dataSource
     _ -> throwM $ UnexpectedMultipleOutputs
 
-checkAndGetFiles :: Bool -> GEvalSpecification -> IO (SourceSpec, SourceSpec, [SourceSpec])
-checkAndGetFiles forceInput gevalSpec = do
+checkAndGetDataSources :: Bool -> GEvalSpecification -> IO [DataSource]
+checkAndGetDataSources forceInput gevalSpec = do
   ess <- getSmartSourceSpec expectedTestDirectory defaultExpectedFile expectedFile
   case ess of
     Left NoSpecGiven -> throwM $ NoExpectedFile expectedFile
@@ -348,7 +335,22 @@ checkAndGetFiles forceInput gevalSpec = do
                throwM $ NoOutFile outFile
              Right outSource -> do
                return [outSource]
-       return (inputSource, expectedSource, osss)
+
+       mInHeader <- readHeaderFileWrapper $ getInHeader gevalSpec
+       mOutHeader <- readHeaderFileWrapper $ getOutHeader gevalSpec
+
+       let chDataSource = ChallengeDataSource {
+        challengeDataSourceInput = inputSource,
+        challengeDataSourceExpected = expectedSource,
+        challengeDataSourceSelector = mSelector,
+        challengeDataSourcePreprocess = preprocess,
+        challengeDataSourceFilter = Nothing,
+        challengeDataSourceInHeader = mInHeader,
+        challengeDataSourceOutHeader = mOutHeader }
+
+       return $ Prelude.map (\oss -> DataSource {
+                          dataSourceChallengeData = chDataSource,
+                          dataSourceOut = oss}) osss
     where expectedTestDirectory = expectedDirectory </> testName
           outTestDirectory = outDirectory </> testName
           expectedDirectory = getExpectedDirectory gevalSpec
@@ -359,6 +361,9 @@ checkAndGetFiles forceInput gevalSpec = do
           inputFile = gesInputFile gevalSpec
           schemes = gesMetrics gevalSpec
 
+          mSelector = gesSelector gevalSpec
+          preprocess = gesPreprocess gevalSpec
+
 checkSingleOut :: FilePath -> FilePath -> IO (Either SmartSourceError SourceSpec)
 checkSingleOut outTestDirectory outFile
   | outFile == defaultOutFile = do
diff --git a/src/GEval/LineByLine.hs b/src/GEval/LineByLine.hs
index 8b28bc9..3df74a1 100644
--- a/src/GEval/LineByLine.hs
+++ b/src/GEval/LineByLine.hs
@@ -474,26 +474,11 @@ runLineByLineGeneralized ordering spec consum = do
       references <- readReferences referencesFp
       return $ Just references
     Nothing -> return Nothing
-  (inputFilePath, expectedFilePath, outFilePath) <- checkAndGetFilesSingleOut True spec
-  mInHeader <- readHeaderFileWrapper $ getInHeader spec
-  mOutHeader <- readHeaderFileWrapper $ getOutHeader spec
-  let mOutHeader = Nothing
-  let chDataSource = ChallengeDataSource {
-        challengeDataSourceInput = inputFilePath,
-        challengeDataSourceExpected = expectedFilePath,
-        challengeDataSourceSelector = mSelector,
-        challengeDataSourcePreprocess = preprocess,
-        challengeDataSourceFilter = Nothing,
-        challengeDataSourceInHeader = mInHeader,
-        challengeDataSourceOutHeader = mOutHeader }
-  let dataSource = DataSource {
-        dataSourceChallengeData = chDataSource,
-        dataSourceOut = outFilePath }
+  dataSource' <- checkAndGetDataSource True spec
+  let dataSource = addPreprocessing (applyPreprocessingOperations scheme) dataSource'
   gevalLineByLineCore metric dataSource (sorter ordering .| consum mReferences)
   where metric = gesMainMetric spec
         scheme = gesMainScheme spec
-        mSelector = gesSelector spec
-        preprocess = (gesPreprocess spec) . (applyPreprocessingOperations scheme)
         sorter KeepTheOriginalOrder = doNothing
         sorter ordering = gobbleAndDo $ sortBy (sortOrder ordering (getMetricOrdering metric))
         sortOrder FirstTheWorst TheHigherTheBetter = compareScores
@@ -540,21 +525,14 @@ runOracleItemBased spec = runMultiOutputGeneralized spec consum
 
 runMultiOutputGeneralized :: GEvalSpecification -> ConduitT [LineRecord] Void (ResourceT IO) () -> IO ()
 runMultiOutputGeneralized spec consum = do
-  (inputSource, expectedSource, outSource) <- checkAndGetFilesSingleOut True spec
+  dataSource' <- checkAndGetDataSource True spec
+  let dataSource = addPreprocessing (applyPreprocessingOperations scheme) dataSource'
   let (Just altOuts) = gesAltOutFiles spec
   altSourceSpecs' <- mapM (getSmartSourceSpec ((gesOutDirectory spec) </> (gesTestName spec)) "out.tsv") altOuts
   let altSourceSpecs = rights altSourceSpecs'
+  let outSource = dataSourceOut dataSource
   let sourceSpecs = (outSource:altSourceSpecs)
-  mInHeader <- readHeaderFileWrapper $ getInHeader spec
-  mOutHeader <- readHeaderFileWrapper $ getOutHeader spec
-  let chDataSource = ChallengeDataSource {
-        challengeDataSourceInput = inputSource,
-        challengeDataSourceExpected = expectedSource,
-        challengeDataSourceSelector = mSelector,
-        challengeDataSourcePreprocess = preprocess,
-        challengeDataSourceFilter = Nothing,
-        challengeDataSourceInHeader = mInHeader,
-        challengeDataSourceOutHeader = mOutHeader }
+  let chDataSource = dataSourceChallengeData dataSource
   let sources = Prelude.map (\s -> gevalLineByLineSource metric DataSource {
                                 dataSourceChallengeData = chDataSource,
                                 dataSourceOut = s}) sourceSpecs
@@ -562,8 +540,6 @@ runMultiOutputGeneralized spec consum = do
     (sequenceSources sources .| consum)
   where metric = gesMainMetric spec
         scheme = gesMainScheme spec
-        preprocess = (gesPreprocess spec) . (applyPreprocessingOperations scheme)
-        mSelector = gesSelector spec
 
 runMostWorseningFeatures :: ResultOrdering -> FilePath -> GEvalSpecification -> BlackBoxDebuggingOptions -> IO ()
 runMostWorseningFeatures ordering otherOut spec bbdo = do
@@ -585,29 +561,17 @@ runMostWorseningFeatures ordering otherOut spec bbdo = do
 
 runDiffGeneralized :: ResultOrdering -> FilePath -> GEvalSpecification -> (Maybe References -> ConduitT (LineRecord, LineRecord) Void (ResourceT IO) a) -> IO a
 runDiffGeneralized ordering otherOut spec consum = do
-  (inputSource, expectedSource, outSource) <- checkAndGetFilesSingleOut True spec
+  dataSourceB <- checkAndGetDataSource True spec
   ooss <- getSmartSourceSpec ((gesOutDirectory spec) </> (gesTestName spec)) "out.tsv" otherOut
-  mInHeader <- readHeaderFileWrapper $ getInHeader spec
-  mOutHeader <- readHeaderFileWrapper $ getOutHeader spec
   case ooss of
     Left NoSpecGiven -> throwM $ NoOutFile otherOut
     Left (NoFile fp) -> throwM $ NoOutFile fp
     Left (NoDirectory d) -> throwM $ NoOutFile otherOut
     Right otherOutSource -> do
-      let chDataSource = ChallengeDataSource {
-            challengeDataSourceInput = inputSource,
-            challengeDataSourceExpected = expectedSource,
-            challengeDataSourceSelector = mSelector,
-            challengeDataSourcePreprocess = preprocess,
-            challengeDataSourceFilter = Nothing,
-            challengeDataSourceInHeader = mInHeader,
-            challengeDataSourceOutHeader = mOutHeader }
+      let chDataSource = dataSourceChallengeData dataSourceB
       let dataSourceA = DataSource {
             dataSourceChallengeData = chDataSource,
             dataSourceOut = otherOutSource}
-      let dataSourceB = DataSource {
-            dataSourceChallengeData = chDataSource,
-            dataSourceOut = outSource}
       let sourceA = gevalLineByLineSource metric dataSourceA
       let sourceB = gevalLineByLineSource metric dataSourceB
       runResourceT $ runConduit $