Java support of casting string from/to decimal (#7623)

This pull request provided Java side support of casting string from/to decimal, which is required by spark-rapids.

Although parsing of string formatted as scientific notation to decimal has not been supported yet by cuDF, we are able to implement string to decimal conversion at spark-rapids side through a two-steps hack: 
1. casting string to float 
2. casting float to decimal

In addition, this pull request also addressed issue #6795.

Authors:
  - Alfred Xu (@sperlingxx)

Approvers:
  - Robert (Bobby) Evans (@revans2)

URL: #7623

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

@@ -1164,6 +1164,17 @@ public static ColumnVector decimalFromInts(int scale, int... values) {
     }
   }
 
+  /**
+   * Create a new decimal vector from boxed unscaled values (Integer array) and scale.
+   * The created vector is of type DType.DECIMAL32, whose max precision is 9.
+   * Compared with scale of [[java.math.BigDecimal]], the scale here represents the opposite meaning.
+   */
+  public static ColumnVector decimalFromBoxedInts(int scale, Integer... values) {
+    try (HostColumnVector host = HostColumnVector.decimalFromBoxedInts(scale, values)) {
+      return host.copyToDevice();
+    }
+  }
+
   /**
    * Create a new decimal vector from unscaled values (long array) and scale.
    * The created vector is of type DType.DECIMAL64, whose max precision is 18.
@@ -1175,6 +1186,17 @@ public static ColumnVector decimalFromLongs(int scale, long... values) {
     }
   }
 
+  /**
+   * Create a new decimal vector from boxed unscaled values (Long array) and scale.
+   * The created vector is of type DType.DECIMAL64, whose max precision is 18.
+   * Compared with scale of [[java.math.BigDecimal]], the scale here represents the opposite meaning.
+   */
+  public static ColumnVector decimalFromBoxedLongs(int scale, Long... values) {
+    try (HostColumnVector host = HostColumnVector.decimalFromBoxedLongs(scale, values)) {
+      return host.copyToDevice();
+    }
+  }
+
   /**
    * Create a new decimal vector from double floats with specific DecimalType and RoundingMode.
    * All doubles will be rescaled if necessary, according to scale of input DecimalType and RoundingMode.

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

@@ -481,6 +481,23 @@ public static HostColumnVector decimalFromInts(int scale, int... values) {
     return build(DType.create(DType.DTypeEnum.DECIMAL32, scale), values.length, (b) -> b.appendUnscaledDecimalArray(values));
   }
 
+  /**
+   * Create a new decimal vector from boxed unscaled values (Integer array) and scale.
+   * The created vector is of type DType.DECIMAL32, whose max precision is 9.
+   * Compared with scale of [[java.math.BigDecimal]], the scale here represents the opposite meaning.
+   */
+  public static HostColumnVector decimalFromBoxedInts(int scale, Integer... values) {
+    return build(DType.create(DType.DTypeEnum.DECIMAL32, scale), values.length, (b) -> {
+      for (Integer v : values) {
+        if (v == null) {
+          b.appendNull();
+        } else {
+          b.appendUnscaledDecimal(v);
+        }
+      }
+    });
+  }
+
   /**
    * Create a new decimal vector from unscaled values (long array) and scale.
    * The created vector is of type DType.DECIMAL64, whose max precision is 18.
@@ -490,6 +507,23 @@ public static HostColumnVector decimalFromLongs(int scale, long... values) {
     return build(DType.create(DType.DTypeEnum.DECIMAL64, scale), values.length, (b) -> b.appendUnscaledDecimalArray(values));
   }
 
+  /**
+   * Create a new decimal vector from boxed unscaled values (Long array) and scale.
+   * The created vector is of type DType.DECIMAL64, whose max precision is 18.
+   * Compared with scale of [[java.math.BigDecimal]], the scale here represents the opposite meaning.
+   */
+  public static HostColumnVector decimalFromBoxedLongs(int scale, Long... values) {
+    return build(DType.create(DType.DTypeEnum.DECIMAL64, scale), values.length, (b) -> {
+      for (Long v : values) {
+        if (v == null) {
+          b.appendNull();
+        } else {
+          b.appendUnscaledDecimal(v);
+        }
+      }
+    });
+  }
+
   /**
    * Create a new decimal vector from double floats with specific DecimalType and RoundingMode.
    * All doubles will be rescaled if necessary, according to scale of input DecimalType and RoundingMode.

java/src/main/native/src/ColumnViewJni.cpp

@@ -42,6 +42,7 @@
 #include <cudf/strings/contains.hpp>
 #include <cudf/strings/convert/convert_booleans.hpp>
 #include <cudf/strings/convert/convert_datetime.hpp>
+#include <cudf/strings/convert/convert_fixed_point.hpp>
 #include <cudf/strings/convert/convert_floats.hpp>
 #include <cudf/strings/convert/convert_integers.hpp>
 #include <cudf/strings/convert/convert_urls.hpp>
@@ -712,6 +713,10 @@ JNIEXPORT jlong JNICALL Java_ai_rapids_cudf_ColumnView_castTo(JNIEnv *env, jclas
         case cudf::type_id::UINT64:
           result = cudf::strings::from_integers(*column);
           break;
+        case cudf::type_id::DECIMAL32:
+        case cudf::type_id::DECIMAL64:
+          result = cudf::strings::from_fixed_point(*column);
+          break;
         default: JNI_THROW_NEW(env, "java/lang/IllegalArgumentException", "Invalid data type", 0);
       }
     } else if (column->type().id() == cudf::type_id::STRING) {
@@ -733,6 +738,10 @@ JNIEXPORT jlong JNICALL Java_ai_rapids_cudf_ColumnView_castTo(JNIEnv *env, jclas
         case cudf::type_id::UINT64:
           result = cudf::strings::to_integers(*column, n_data_type);
           break;
+        case cudf::type_id::DECIMAL32:
+        case cudf::type_id::DECIMAL64:
+          result = cudf::strings::to_fixed_point(*column, n_data_type);
+          break;
         default: JNI_THROW_NEW(env, "java/lang/IllegalArgumentException", "Invalid data type", 0);
       }
     } else if (cudf::is_timestamp(n_data_type) && cudf::is_numeric(column->type())) {

java/src/test/java/ai/rapids/cudf/ColumnVectorTest.java

@@ -2226,6 +2226,73 @@ void testCastBoolToString() {
     testCastFixedWidthToStringsAndBack(DType.BOOL8, () -> ColumnVector.fromBoxedBooleans(booleans), () -> ColumnVector.fromStrings(stringBools));
   }
 
+  @Test
+  void testCastDecimal32ToString() {
+
+    Integer[] unScaledValues = {0, null, 3, 2, -43, null, 5234, -73451, 348093, -234810};
+    String[] strDecimalValues = new String[unScaledValues.length];
+    for (int scale : new int[]{-2, -1, 0, 1, 2}) {
+      for (int i = 0; i < strDecimalValues.length; i++) {
+        Long value = unScaledValues[i] == null ? null : Long.valueOf(unScaledValues[i]);
+        strDecimalValues[i] = dumpDecimal(value, scale);
+      }
+
+      testCastFixedWidthToStringsAndBack(DType.create(DType.DTypeEnum.DECIMAL32, scale),
+          () -> ColumnVector.decimalFromBoxedInts(scale, unScaledValues),
+          () -> ColumnVector.fromStrings(strDecimalValues));
+    }
+  }
+
+  @Test
+  void testCastDecimal64ToString() {
+
+    Long[] unScaledValues = {0l, null, 3l, 2l, -43l, null, 234802l, -94582l, 1234208124l, -2342348023812l};
+    String[] strDecimalValues = new String[unScaledValues.length];
+    for (int scale : new int[]{-5, -2, -1, 0, 1, 2, 5}) {
+      for (int i = 0; i < strDecimalValues.length; i++) {
+        strDecimalValues[i] = dumpDecimal(unScaledValues[i], scale);
+        System.out.println(strDecimalValues[i]);
+      }
+
+      testCastFixedWidthToStringsAndBack(DType.create(DType.DTypeEnum.DECIMAL64, scale),
+          () -> ColumnVector.decimalFromBoxedLongs(scale, unScaledValues),
+          () -> ColumnVector.fromStrings(strDecimalValues));
+    }
+  }
+
+  /**
+   * Helper function to create decimal strings which can be processed by castStringToDecimal functor.
+   * We can not simply create decimal string via `String.valueOf`, because castStringToDecimal doesn't
+   * support scientific notations so far.
+   *
+   * issue for scientific notation: https://github.com/rapidsai/cudf/issues/7665
+   */
+  private static String dumpDecimal(Long unscaledValue, int scale) {
+    if (unscaledValue == null) return null;
+
+    StringBuilder builder = new StringBuilder();
+    if (unscaledValue < 0) builder.append('-');
+    String absValue = String.valueOf(Math.abs(unscaledValue));
+
+    if (scale >= 0) {
+      builder.append(absValue);
+      for (int i = 0; i < scale; i++) builder.append('0');
+      return builder.toString();
+    }
+
+    if (absValue.length() <= -scale) {
+      builder.append('0').append('.');
+      for (int i = 0; i < -scale - absValue.length(); i++) builder.append('0');
+      builder.append(absValue);
+    } else {
+      int split = absValue.length() + scale;
+      builder.append(absValue.substring(0, split))
+          .append('.')
+          .append(absValue.substring(split));
+    }
+    return builder.toString();
+  }
+
   private static <T> String[] getStringArray(T[] input) {
     String[] result = new String[input.length];
     for (int i = 0 ; i < input.length ; i++) {