Allow filtering output by diff action

DIFF.md

@@ -419,9 +419,9 @@ spark-submit --packages com.github.scopt:scopt_2.13:4.1.0 spark-extension_2.13-2
 ```
 
 ```
-Spark Diff app (2.7.0-3.4)
+Spark Diff app (2.10.0-3.4)
 
-Usage: spark-extension_2.13-2.7.0-3.4.jar [options] left right diff
+Usage: spark-extension_2.13-2.10.0-3.4.jar [options] left right diff
 
   left                     file path (requires format option) or table name to read left dataframe
   right                    file path (requires format option) or table name to read right dataframe
@@ -430,10 +430,10 @@ Usage: spark-extension_2.13-2.7.0-3.4.jar [options] left right diff
 Examples:
 
   - Diff CSV files 'left.csv' and 'right.csv' and write result into CSV file 'diff.csv':
-    spark-submit --packages com.github.scopt:scopt_2.13:4.1.0 spark-extension_2.13-2.7.0-3.4.jar --format csv left.csv right.csv diff.csv
+    spark-submit --packages com.github.scopt:scopt_2.13:4.1.0 spark-extension_2.13-2.10.0-3.4.jar --format csv left.csv right.csv diff.csv
 
   - Diff CSV file 'left.csv' with Parquet file 'right.parquet' with id column 'id', and write result into Hive table 'diff':
-    spark-submit --packages com.github.scopt:scopt_2.13:4.1.0 spark-extension_2.13-2.7.0-3.4.jar --left-format csv --right-format parquet --hive --id id left.csv right.parquet diff
+    spark-submit --packages com.github.scopt:scopt_2.13:4.1.0 spark-extension_2.13-2.10.0-3.4.jar --left-format csv --right-format parquet --hive --id id left.csv right.parquet diff
 
 Spark session
   --master <master>        Spark master (local, yarn, ...), not needed with spark-submit
@@ -457,6 +457,7 @@ Input and output
   --id <name>              id column name
   --ignore <name>          ignore column name
   --save-mode <save-mode>  save mode for writing output (Append, Overwrite, ErrorIfExists, Ignore, default ErrorIfExists)
+  --filter <filter>        Filters for rows with these diff actions, with default diffing options use 'N', 'I', 'D', or 'C' (see 'Diffing options' section)
 
 Diffing options
   --diff-column <name>     column name for diff column (default 'diff')

src/main/scala/uk/co/gresearch/spark/diff/App.scala

@@ -16,6 +16,7 @@
 
 package uk.co.gresearch.spark.diff
 
+import org.apache.spark.sql.functions.col
 import org.apache.spark.sql.{DataFrame, SaveMode, SparkSession}
 import scopt.OptionParser
 import uk.co.gresearch._
@@ -44,6 +45,7 @@ object App {
                      ids: Seq[String] = Seq.empty,
                      ignore: Seq[String] = Seq.empty,
                      saveMode: SaveMode = SaveMode.ErrorIfExists,
+                     filter: Set[String] = Set.empty,
                      diffOptions: DiffOptions = DiffOptions.default)
 
   // read options from args
@@ -171,6 +173,12 @@ object App {
       .valueName("<save-mode>")
       .action((x, c) => c.copy(saveMode = SaveMode.valueOf(x)))
       .text(s"save mode for writing output (${SaveMode.values().mkString(", ")}, default ${Options().saveMode})")
+    opt[String]("filter")
+      .unbounded()
+      .optional()
+      .valueName("<filter>")
+      .action((x, c) => c.copy(filter = c.filter + x))
+      .text(s"Filters for rows with these diff actions, with default diffing options use 'N', 'I', 'D', or 'C' (see 'Diffing options' section)")
 
     note("")
     note("Diffing options")
@@ -236,8 +244,9 @@ object App {
       .when(schema.isDefined).call(_.schema(schema.get))
       .when(format.isDefined).either(_.load(path)).or(_.table(path))
 
-  def write(df: DataFrame, format: Option[String], path: String, options: Map[String, String], saveMode: SaveMode): Unit =
-    df.write
+  def write(df: DataFrame, format: Option[String], path: String, options: Map[String, String], saveMode: SaveMode, filter: Set[String], diffOptions: DiffOptions): Unit =
+    df.when(filter.nonEmpty).call(_.where(col(diffOptions.diffColumn).isInCollection(filter)))
+      .write
       .when(format.isDefined).call(_.format(format.get))
       .options(options)
       .mode(saveMode)
@@ -261,6 +270,6 @@ object App {
     val left = read(spark, options.leftFormat, options.leftPath.get, options.leftSchema, options.leftOptions)
     val right = read(spark, options.rightFormat, options.rightPath.get, options.rightSchema, options.rightOptions)
     val diff = left.diff(right, options.diffOptions, options.ids, options.ignore)
-    write(diff, options.outputFormat, options.outputPath.get, options.outputOptions, options.saveMode)
+    write(diff, options.outputFormat, options.outputPath.get, options.outputOptions, options.saveMode, options.filter, options.diffOptions)
   }
 }

src/test/scala/uk/co/gresearch/spark/diff/AppSuite.scala

@@ -52,4 +52,35 @@ class AppSuite extends AnyFunSuite with SparkTestSession {
       assert(actual.orderBy($"id").collect() === DiffSuite.expectedDiff)
     }
   }
+
+  Seq(Set("I"), Set("C"), Set("D"), Set("N"), Set("I", "C", "D")).foreach { filter =>
+    test(s"run app with filter ${filter.mkString("[", ",", "]")}") {
+      withTempPath { path =>
+        // write left dataframe as parquet
+        val leftPath = new File(path, "left.parquet").getAbsolutePath
+        DiffSuite.left(spark).write.parquet(leftPath)
+
+        // write right dataframe as csv
+        val rightPath = new File(path, "right.parquet").getAbsolutePath
+        DiffSuite.right(spark).write.parquet(rightPath)
+
+        // launch app
+        val outputPath = new File(path, "diff.parquet").getAbsolutePath
+        App.main(Array(
+          "--format", "parquet",
+          "--id", "id",
+        ) ++ filter.toSeq.flatMap(f => Array("--filter", f)) ++ Array(
+          leftPath,
+          rightPath,
+          outputPath
+        ))
+
+        // assert written diff
+        val actual = spark.read.parquet(outputPath).orderBy($"id").collect()
+        val expected = DiffSuite.expectedDiff.filter(row => filter.contains(row.getString(0)))
+        assert(actual === expected)
+        assert(expected.nonEmpty)
+      }
+    }
+  }
 }