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case class Person(name: String, age: Int)
case class Couple(p1: String, p2: String)

def sameAgeCouples(
  people: Dataset[Person], 
  couples: Dataset[Couple]
): Dataset[Couple] =
  run {
    for {
      p1 <- liftQuery(people)

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 def flatMap[U](f: T => RDD[U]): RDD[U]

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def flatMap[U](f: T => TraversableOnce[U]): RDD[U]

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SELECT x2.*
FROM
  (SELECT LOWER (x2._1) _1,
          COUNT(*)      _2
   FROM
     (SELECT explode(SPLIT(x1.text, ' ')) _1
      FROM (?) x1) x2
   WHERE x2._1 LIKE (concat('#', '%'))
   GROUP BY LOWER (x2._1)) x10
ORDER BY - (x2._2) ASC NULLS FIRST

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def topHashtags(tweets: RDD[Tweet], n: Int): Array[(String, BigInt)] =
  tweets
    .flatMap(_.text.split("\\s+"))     // split it into words
    .filter(_.startsWith("#"))         // filter hashtag words
    .map(_.toLowerCase)                // normalize hashtags
    .map((_, BigInt(1)))               // create tuples for counting
    .reduceByKey((a, b) => a + b)      // accumulate counters
    .top(n)(Ordering.by(_._2))         // return ordered top hashtags

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def topHashtags(tweets: DataFrame, n: Int): DataFrame =
  tweets
    .select(explode(split($"text", "\\s+"))) // split it into words
    .select(lower($"col") as "word")         // normalize hashtags
    .filter("word like '#%'")                // filter hashtag words
    .groupBy($"word")                        // group by each hashtag
    .agg(count("*") as "count")              // aggregate the count
    .orderBy($"count" desc)                  // order
    .limit(n)                                // limit to top results

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def topHashtags(tweets: Dataset[Tweet], n: Int): Dataset[(String, BigInt)] =
  tweets
    .select($"text".as[String]) // select the text column (Dataframe)
    .flatMap(_.split("\\s+"))   // split it into words    (Dataset)
    .filter(_.startsWith("#"))  // filter hashtag words   (Dataset)
    .map(_.toLowerCase)         // normalize hashtags     (Dataset)
    .groupBy($"value")          // group by each hashtag  (Dataframe)
    .agg(count("*") as "count") // aggregate the count    (Dataframe)
    .orderBy($"count" desc)     // order                  (Datafeame)
    .limit(n)                   // limit to top results   (Dataframe) 

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def topHashtags(tweets: Dataset[Tweet], n: Int): Dataset[(String, Long)] =
  run {                               // produce a dataset from the Quill query
    liftQuery(tweets)                 // trasform the dataset into a Quill query
      .concatMap(_.text.split(" "))   // split into words and unnest results
      .filter(_.startsWith("#"))      // filter hashtag words
      .map(_.toLowerCase)             // normalize hashtags
      .groupBy(word => word)          // group by each hashtag
      .map {                          // map word list to its count
        case (word, list) => 
          (word, list.size)

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Please help us validate Quill 2.0.0-SNAPSHOT so we can make the final release. Steps:

1. Read the migration notes
2. Add the snapshots repo to your sbt build: resolvers += Resolver.sonatypeRepo("snapshots")
3. Update the Quill version to 2.0.0-SNAPSHOT
4. Fix the compilation errors, feel free to ask questions on the gitter channel
5. Let us know the results

This version has 0️⃣ (yes, ZERO!) known bugs

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/**
 * 
 * THIS IS JUST A DSL PROTOTYPE
 * 
 * First tentative of a DSL for defining macro transformations in Java.
 * There's a lot of noise because of the absence of pattern matching and tuples.
 * This is a prototype of one of the if/else transformations in Monadless:
 *
 *          case q"if($cond) $ifTrue else $ifFalse" =>
 *           (ifTrue, ifFalse) match {