Add Java API for Concatenate strings with separator [skip ci]

java/src/main/java/ai/rapids/cudf/ColumnVector.java

@@ -500,7 +500,8 @@ public static ColumnVector stringConcatenate(ColumnView[] columns) {
 
   /**
    * Concatenate columns of strings together, combining a corresponding row from each column into
-   * a single string row of a new column.
+   * a single string row of a new column. This version includes the separator for null rows
+   * if 'narep' is valid.
    * @param separator string scalar inserted between each string being merged.
    * @param narep string scalar indicating null behavior. If set to null and any string in the row
    *              is null the resulting string will be null. If not null, null values in any column
@@ -509,20 +510,89 @@ public static ColumnVector stringConcatenate(ColumnView[] columns) {
    * @return A new java column vector containing the concatenated strings.
    */
   public static ColumnVector stringConcatenate(Scalar separator, Scalar narep, ColumnView[] columns) {
+    return stringConcatenate(separator, narep, columns, true);
+  }
+
+  /**
+   * Concatenate columns of strings together, combining a corresponding row from each column into
+   * a single string row of a new column.
+   * @param separator string scalar inserted between each string being merged.
+   * @param narep string scalar indicating null behavior. If set to null and any string in the row
+   *              is null the resulting string will be null. If not null, null values in any column
+   *              will be replaced by the specified string.
+   * @param columns array of columns containing strings, must be non-empty
+   * @param separateNulls if true, then the separator is included for null rows if
+   *                       `narep` is valid.
+   * @return A new java column vector containing the concatenated strings.
+   */
+  public static ColumnVector stringConcatenate(Scalar separator, Scalar narep, ColumnView[] columns,
+      boolean separateNulls) {
     assert columns != null : "input columns should not be null";
     assert columns.length > 0 : "input columns should not be empty";
     assert separator != null : "separator scalar provided may not be null";
     assert separator.getType().equals(DType.STRING) : "separator scalar must be a string scalar";
     assert narep != null : "narep scalar provided may not be null";
     assert narep.getType().equals(DType.STRING) : "narep scalar must be a string scalar";
 
-    long[] column_views = new long[columns.length];
+    long[] columnViews = new long[columns.length];
+    for(int i = 0; i < columns.length; i++) {
+      assert columns[i] != null : "Column vectors passed may not be null";
+      columnViews[i] = columns[i].getNativeView();
+    }
+
+    return new ColumnVector(stringConcatenation(columnViews, separator.getScalarHandle(),
+        narep.getScalarHandle(), separateNulls));
+  }
+
+  /**
+   * Concatenate columns of strings together using a separator specified for each row
+   * and returns the result as a string column. If the row separator for a given row is null,
+   * output column for that row is null. Null column values for a given row are skipped.
+   * @param columns array of columns containing strings
+   * @param sepCol strings column that provides the separator for a given row
+   * @return A new java column vector containing the concatenated strings with separator between.
+   */
+  public static ColumnVector stringConcatenate(ColumnView[] columns, ColumnView sepCol) {
+    try (Scalar nullString = Scalar.fromString(null);
+         Scalar emptyString = Scalar.fromString("")) {
+      return stringConcatenate(columns, sepCol, nullString, emptyString, false);
+    }
+  }
+
+  /**
+   * Concatenate columns of strings together using a separator specified for each row
+   * and returns the result as a string column. If the row separator for a given row is null,
+   * output column for that row is null unless separatorNarep is provided.
+   * The separator is applied between two output row values if the separateNulls
+   * is `YES` or only between valid rows if separateNulls is `NO`.
+   * @param columns array of columns containing strings
+   * @param sepCol strings column that provides the separator for a given row
+   * @param separatorNarep string scalar indicating null behavior when a separator is null.
+   *                        If set to null and the separator is null the resulting string will
+   *                        be null. If not null, this string will be used in place of a null
+   *                        separator.
+   * @param colNarep string that should be used in place of any null strings
+   *                  found in any column.
+   * @param separateNulls if true, then the separator is included for null rows if
+   *                       `colNarep` is valid.
+   * @return A new java column vector containing the concatenated strings with separator between.
+   */
+  public static ColumnVector stringConcatenate(ColumnView[] columns,
+      ColumnView sepCol, Scalar separatorNarep, Scalar colNarep, boolean separateNulls) {
+    assert columns.length >= 1 : ".stringConcatenate() operation requires at least 1 column";
+    assert separatorNarep != null : "separator narep scalar provided may not be null";
+    assert colNarep != null : "column narep scalar provided may not be null";
+    assert separatorNarep.getType().equals(DType.STRING) : "separator naprep scalar must be a string scalar";
+    assert colNarep.getType().equals(DType.STRING) : "column narep scalar must be a string scalar";
+
+    long[] columnViews = new long[columns.length];
     for(int i = 0; i < columns.length; i++) {
       assert columns[i] != null : "Column vectors passed may not be null";
-      column_views[i] = columns[i].getNativeView();
+      columnViews[i] = columns[i].getNativeView();
     }
 
-    return new ColumnVector(stringConcatenation(column_views, separator.getScalarHandle(), narep.getScalarHandle()));
+    return new ColumnVector(stringConcatenationSepCol(columnViews, sepCol.getNativeView(),
+      separatorNarep.getScalarHandle(), colNarep.getScalarHandle(), separateNulls));
   }
 
   /**
@@ -717,14 +787,39 @@ private static native long makeList(long[] handles, long typeHandle, int scale,
    *
    * @param columnViews array of longs holding the native handles of the column_views to combine.
    * @param separator   string scalar inserted between each string being merged, may not be null.
-   * @param narep       string scalar indicating null behavior. If set to null and any string in the row is null
-   *                    the resulting string will be null. If not null, null values in any column will be
-   *                    replaced by the specified string. The underlying value in the string scalar may be null,
-   *                    but the object passed in may not.
+   * @param narep       string scalar indicating null behavior. If set to null and any string in
+   *                    the row is null the resulting string will be null. If not null, null
+   *                    values in any column will be replaced by the specified string. The
+   *                    underlying value in the string scalar may be null, but the object passed
+   *                    in may not.
+   * @param separate_nulls boolean if true, then the separator is included for null rows if
+   *                       `narep` is valid.
    * @return native handle of the resulting cudf column, used to construct the Java column
    * by the stringConcatenate method.
    */
-  private static native long stringConcatenation(long[] columnViews, long separator, long narep);
+  private static native long stringConcatenation(long[] columnViews, long separator, long narep,
+                                                 boolean separate_nulls);
+
+  /**
+   * Native method to concatenate columns of strings together using a separator specified for each row
+   * and returns the result as a string column.
+   * @param columns array of longs holding the native handles of the column_views to combine.
+   * @param sep_column long holding the native handle of the strings_column_view used as separators.
+   * @param separator_narep string scalar indicating null behavior when a separator is null.
+   *                        If set to null and the separator is null the resulting string will
+   *                        be null. If not null, this string will be used in place of a null
+   *                        separator.
+   * @param col_narep string String scalar that should be used in place of any null strings
+   *                         found in any column.
+   * @param separate_nulls boolean if true, then the separator is included for null rows if
+   *                       `col_narep` is valid.
+   * @return native handle of the resulting cudf column, used to construct the Java column.
+   */
+  private static native long stringConcatenationSepCol(long[] columnViews,
+                                                       long sep_column,
+                                                       long separator_narep,
+                                                       long col_narep,
+                                                       boolean separate_nulls);
 
   /**
    * Native method to hash each row of the given table. Hashing function dispatched on the

java/src/main/java/ai/rapids/cudf/ColumnView.java

@@ -2116,6 +2116,85 @@ public final ColumnVector substring(ColumnView start, ColumnView end) {
     return new ColumnVector(substringColumn(getNativeView(), start.getNativeView(), end.getNativeView()));
   }
 
+  /**
+   * Given a lists column of strings (each row is a list of strings), concatenates the strings
+   * within each row and returns a single strings column result. Each new string is created by
+   * concatenating the strings from the same row (same list element) delimited by the separator
+   * provided. This version of the function relaces nulls with empty string and returns null
+   * for empty list.
+   * @param list_column column containing lists of strings to concatenate.
+   * @param sep_col strings column that provides separators for concatenation.
+   * @return A new java column vector containing the concatenated strings with separator between.
+   */
+  public final ColumnVector stringConcatenateListElements(ColumnView sep_col) {
+    try (Scalar nullString = Scalar.fromString(null);
+         Scalar emptyString = Scalar.fromString("")) {
+      return stringConcatenateListElements(sep_col, nullString, emptyString,
+          false, false);
+    }
+  }
+
+  /**
+   * Given a lists column of strings (each row is a list of strings), concatenates the strings
+   * within each row and returns a single strings column result.
+   * Each new string is created by concatenating the strings from the same row (same list element)
+   * delimited by the row separator provided in the sep_col strings column.
+   * @param sep_col strings column that provides separators for concatenation.
+   * @param separator_narep string scalar indicating null behavior when a separator is null.
+   *                        If set to null and the separator is null the resulting string will
+   *                        be null. If not null, this string will be used in place of a null
+   *                        separator.
+   * @param string_narep string that should be used to replace null strings in any non-null list
+   *                     row. If set to null and the string is null the resulting string will
+   *                     be null. If not null, this string will be used in place of a null value.
+   * @param separate_nulls if true, then the separator is included for null rows if
+   *                       `string_narep` is valid.
+   * @param empty_string_output_if_empty_list if set to true, any input row that is an empty list
+   *                          will result in an empty string. Otherwise, it will result in a null.
+   * @return A new java column vector containing the concatenated strings with separator between.
+   */
+  public final ColumnVector stringConcatenateListElements(ColumnView sep_col,
+      Scalar separator_narep, Scalar string_narep, boolean separate_nulls,
+      boolean empty_string_output_if_empty_list) {
+    assert type.equals(DType.LIST) : "column type must be a list";
+    assert separator_narep != null : "separator narep scalar provided may not be null";
+    assert string_narep != null : "string narep scalar provided may not be null";
+    assert separator_narep.getType().equals(DType.STRING) : "separator naprep scalar must be a string scalar";
+    assert string_narep.getType().equals(DType.STRING) : "string narep scalar must be a string scalar";
+
+    return new ColumnVector(stringConcatenationListElementsSepCol(getNativeView(),
+      sep_col.getNativeView(), separator_narep.getScalarHandle(), string_narep.getScalarHandle(),
+      separate_nulls, empty_string_output_if_empty_list));
+  }
+
+  /**
+   * Given a lists column of strings (each row is a list of strings), concatenates the strings
+   * within each row and returns a single strings column result. Each new string is created by
+   * concatenating the strings from the same row (same list element) delimited by the
+   * separator provided.
+   * @param separator string scalar inserted between each string being merged.
+   * @param narep string scalar indicating null behavior. If set to null and any string in the row
+   *              is null the resulting string will be null. If not null, null values in any
+   *              column will be replaced by the specified string. The underlying value in the
+   *              string scalar may be null, but the object passed in may not.
+   * @param separate_nulls if true, then the separator is included for null rows if
+   *                       `narep` is valid.
+   * @param empty_string_output_if_empty_list if set to true, any input row that is an empty list
+   *                          will result in an empty string. Otherwise, it will result in a null.
+   * @return A new java column vector containing the concatenated strings with separator between.
+   */
+  public final ColumnVector stringConcatenateListElements(Scalar separator,
+      Scalar narep, boolean separate_nulls, boolean empty_string_output_if_empty_list) {
+    assert type.equals(DType.LIST) : "column type must be a list";
+    assert separator != null : "separator scalar provided may not be null";
+    assert narep != null : "column narep scalar provided may not be null";
+    assert narep.getType().equals(DType.STRING) : "narep scalar must be a string scalar";
+
+    return new ColumnVector(stringConcatenationListElements(getNativeView(),
+        separator.getScalarHandle(), narep.getScalarHandle(), separate_nulls,
+        empty_string_output_if_empty_list));
+  }
+
    /**
    * Apply a JSONPath string to all rows in an input strings column.
    *
@@ -2712,6 +2791,60 @@ static DeviceMemoryBufferView getOffsetsBuffer(long viewHandle) {
    */
   private static native long stringTimestampToTimestamp(long viewHandle, int unit, String format);
 
+  /**
+   * Native method to concatenate a list column of strings (each row is a list of strings),
+   * concatenates the strings within each row and returns a single strings column result.
+   * Each new string is created by concatenating the strings from the same row (same list element)
+   * delimited by the row separator provided in the `separators` strings column.
+   * @param listColumnHandle long holding the native handle of the column containing lists of strings
+   *                         to concatenate.
+   * @param sepColumn long holding the native handle of the strings column that provides separators
+   *                  for concatenation.
+   * @param separatorNarep string scalar indicating null behavior when a separator is null.
+   *                       If set to null and the separator is null the resulting string will
+   *                       be null. If not null, this string will be used in place of a null
+   *                       separator.
+   * @param colNarep string String scalar that should be used in place of any null strings
+   *                 found in any column.
+   * @param separateNulls boolean if true, then the separator is included for null rows if
+   *                     `colNarep` is valid.
+   * @param emptyStringOutputIfEmptyList boolean if true, any input row that is an empty list
+   *                                     will result in an empty string. Otherwise, it will
+   *                                     result in a null.
+   * @return native handle of the resulting cudf column, used to construct the Java column.
+   */
+  private static native long stringConcatenationListElementsSepCol(long listColumnHandle,
+                                                                   long sepColumn,
+                                                                   long separatorNarep,
+                                                                   long colNarep,
+                                                                   boolean separateNulls,
+                                                                   boolean emptyStringOutputIfEmptyList);
+
+  /**
+   * Native method to concatenate a list column of strings (each row is a list of strings),
+   * concatenates the strings within each row and returns a single strings column result.
+   * Each new string is created by concatenating the strings from the same row (same list element)
+   * delimited by the separator provided.
+   * @param listColumnHandle long holding the native handle of the column containing lists of strings
+   *                     to concatenate.
+   * @param separator string scalar inserted between each string being merged, may not be null.
+   * @param narep string scalar indicating null behavior. If set to null and any string in the row
+   *              is null the resulting string will be null. If not null, null values in any
+   *              column will be replaced by the specified string. The underlying value in the
+   *              string scalar may be null, but the object passed in may not.
+   * @param separateNulls boolean if true, then the separator is included for null rows if
+   *                      `narep` is valid.
+   * @param emptyStringOutputIfEmptyList boolean if true, any input row that is an empty list
+   *                                     will result in an empty string. Otherwise, it will
+   *                                     result in a null.
+   * @return native handle of the resulting cudf column, used to construct the Java column.
+   */
+  private static native long stringConcatenationListElements(long listColumnHandle,
+                                                             long separator,
+                                                             long narep,
+                                                             boolean separateNulls,
+                                                             boolean emptyStringOutputIfEmptyList);
+
   private static native long getJSONObject(long viewHandle, long scalarHandle) throws CudfException;
 
   /**