Add DataFrame renderers (#328)

Rendering DataFrames as HTML table, like Toree does sometimes

build.sc

@@ -277,6 +277,7 @@ class AlmondSpark(val crossScalaVersion: String) extends CrossSbtModule with Amm
     Deps.scalaKernelApi
       .exclude(("com.lihaoyi", s"ammonite-compiler_$crossScalaVersion"))
       .exclude(("com.lihaoyi", s"ammonite-repl-api_$crossScalaVersion")),
+    Deps.scalatags,
     Deps.sparkSql(scalaVersion())
   )
   def repositoriesTask = T.task {

modules/almond-spark/src/main/scala/almond/spark/DataFrameRenderers.scala

@@ -0,0 +1,30 @@
+package almond.spark
+
+import org.apache.spark.sql.{Dataset, Row}
+
+object DataFrameRenderer {
+
+  // inspired by https://github.com/apache/incubator-toree/blob/5b19aac2e56a56d35c888acc4ed5e549b1f4ed7c/kernel/src/main/scala/org/apache/toree/utils/DataFrameConverter.scala#L47-L59
+  def render(df: Dataset[Row], limit: Int = 10): String = {
+    import scalatags.Text.all._
+    val columnFields = df.schema.fieldNames.toSeq.map(th(_))
+    val columns      = tr(columnFields)
+    val rows = df
+      .rdd
+      .map { row =>
+        val fieldValues = row.toSeq.map(fieldToString).map(td(_))
+        tr(fieldValues)
+      }
+      .take(limit)
+    table(columns, rows).render
+  }
+
+  // https://github.com/apache/incubator-toree/blob/5b19aac2e56a56d35c888acc4ed5e549b1f4ed7c/kernel/src/main/scala/org/apache/toree/utils/DataFrameConverter.scala#L84-L89
+  def fieldToString(any: Any): String =
+    any match {
+      case null        => "null"
+      case seq: Seq[_] => seq.mkString("[", ", ", "]")
+      case _           => any.toString
+    }
+
+}

project/deps.sc

@@ -23,6 +23,7 @@ object Deps {
     ivy"com.github.plokhotnyuk.jsoniter-scala::jsoniter-scala-macros:${Versions.jsoniterScala}"
   def log4j2         = ivy"org.apache.logging.log4j:log4j-core:2.17.2"
   def scalaKernelApi = ivy"sh.almond:::scala-kernel-api:0.14.0-RC6"
+  def scalatags      = ivy"com.lihaoyi::scalatags:0.12.0"
   def sparkSql(sv: String) = {
     val ver =
       if (sv.startsWith("2.12.")) "2.4.0"