[MINOR] Add ToString test for decimal-formatting in toString builtin

src/main/java/org/apache/sysds/runtime/util/DataConverter.java

@@ -884,6 +884,23 @@ private static String dfFormat(DecimalFormat df, double value) {
 		}
 	}
 
+	/**
+	 * Creates a non-grouping {@link DecimalFormat} for printing values. When {@code decimal >= 0}
+	 * both the minimum and maximum fraction digits are pinned to {@code decimal}, so values are
+	 * printed with exactly that many decimals; otherwise the {@link DecimalFormat} defaults apply.
+	 * @param decimal number of decimal places to print, -1 for default
+	 * @return a configured {@link DecimalFormat}
+	 */
+	private static DecimalFormat createDecimalFormat(int decimal) {
+		DecimalFormat df = new DecimalFormat();
+		df.setGroupingUsed(false);
+		if (decimal >= 0) {
+			df.setMinimumFractionDigits(decimal);
+			df.setMaximumFractionDigits(decimal);
+		}
+		return df;
+	}
+
 	public static String toString(MatrixBlock mb) {
 		return toString(mb, false, " ", "\n", mb.getNumRows(), mb.getNumColumns(), 3);
 	}
@@ -913,11 +930,7 @@ public static String toString(MatrixBlock mb, boolean sparse, String separator,
 		if (colsToPrint >= 0)
 			colLength = colsToPrint < clen ? colsToPrint : clen;
 
-		DecimalFormat df = new DecimalFormat();
-		df.setGroupingUsed(false);
-		if (decimal >= 0){
-			df.setMinimumFractionDigits(decimal);
-		}
+		DecimalFormat df = createDecimalFormat(decimal);
 
 		if (sparse){ // Sparse Print Format
 			if (mb.isInSparseFormat()){	// Block is in sparse format
@@ -997,11 +1010,7 @@ public static String toString(TensorBlock tb, boolean sparse, String separator,
 		if (colsToPrint >= 0)
 			colLength = Math.min(colsToPrint, clen);
 
-		DecimalFormat df = new DecimalFormat();
-		df.setGroupingUsed(false);
-		if (decimal >= 0){
-			df.setMinimumFractionDigits(decimal);
-		}
+		DecimalFormat df = createDecimalFormat(decimal);
 
 		if (sparse){ // Sparse Print Format
 			// TODO use sparse iterator for sparse block
@@ -1147,10 +1156,7 @@ public static String toString(FrameBlock fb, boolean sparse, String separator, S
 		sb.append(lineseparator);
 
 		//print data
-		DecimalFormat df = new DecimalFormat();
-		df.setGroupingUsed(false);
-		if (decimal >= 0)
-			df.setMinimumFractionDigits(decimal);
+		DecimalFormat df = createDecimalFormat(decimal);
 
 		Iterator<Object[]> iter = IteratorFactory.getObjectRowIterator(fb, 0, rowLength);
 		while( iter.hasNext() ) {

src/test/java/org/apache/sysds/test/component/frame/FrameToStringTest.java

@@ -19,6 +19,7 @@
 
 package org.apache.sysds.test.component.frame;
 
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 
 import org.apache.sysds.common.Types.ValueType;
@@ -38,6 +39,42 @@ public void test100x100() {
 		FrameBlock f = createFrameBlock();
 		assertTrue(DataConverter.toString(f, false, " ", "\n", 100, 100, 3).length() < 75);
 	}
+
+	@Test
+	public void testDecimalClampsFractionDigits() {
+		FrameBlock f = new FrameBlock(new ValueType[]{ValueType.FP64}, new String[]{"C1"});
+		f.ensureAllocatedColumns(1);
+		f.set(0, 0, 5.244058388023880);
+		// decimal=2 must print exactly two fraction digits, not DecimalFormat's default max of 3
+		String out = DataConverter.toString(f, false, " ", "\n", 1, 1, 2);
+		assertTrue("expected value clamped to 5.24, got: " + out, out.contains("5.24\n"));
+		assertFalse("decimal=2 must not print three digits: " + out, out.contains("5.244"));
+	}
+
+	@Test
+	public void testDecimalPadsAndRounds() {
+		FrameBlock f = new FrameBlock(new ValueType[]{ValueType.FP64}, new String[]{"C1"});
+		f.ensureAllocatedColumns(2);
+		f.set(0, 0, 22.0);                // integer-valued: padded up to the requested digits
+		f.set(1, 0, 5.244058388023880);   // rounded at the last requested digit
+		String out = DataConverter.toString(f, false, " ", "\n", 2, 1, 4);
+		assertTrue("expected 22.0000 padded: " + out, out.contains("22.0000\n"));
+		assertTrue("expected 5.2441 rounded: " + out, out.contains("5.2441\n"));
+	}
+
+	@Test
+	public void testNegativeDecimalUsesDefaultFormatting() {
+		FrameBlock f = new FrameBlock(new ValueType[]{ValueType.FP64}, new String[]{"C1"});
+		f.ensureAllocatedColumns(2);
+		f.set(0, 0, 22.0);                // integer-valued: no fraction digits when unconstrained
+		f.set(1, 0, 5.244058388023880);   // default cap of three fraction digits
+		// decimal < 0 leaves DecimalFormat unconstrained (no min/max fraction digits set)
+		String out = DataConverter.toString(f, false, " ", "\n", 2, 1, -1);
+		assertTrue("expected unpadded 22: " + out, out.contains("22\n"));
+		assertFalse("integer value must not be padded: " + out, out.contains("22.0"));
+		assertTrue("expected default 5.244: " + out, out.contains("5.244\n"));
+		assertFalse("must not print a fourth digit: " + out, out.contains("5.2441"));
+	}
 
 	private FrameBlock createFrameBlock() {
 		FrameBlock f = new FrameBlock(new ValueType[]{ValueType.STRING, ValueType.STRING});

src/test/java/org/apache/sysds/test/component/tensor/TensorToStringTest.java

@@ -0,0 +1,66 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.sysds.test.component.tensor;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.apache.sysds.common.Types.ValueType;
+import org.apache.sysds.runtime.data.TensorBlock;
+import org.apache.sysds.runtime.util.DataConverter;
+import org.junit.Test;
+
+public class TensorToStringTest {
+	@Test
+	public void testDecimalClampsFractionDigits() {
+		TensorBlock tb = new TensorBlock(ValueType.FP64, new int[]{1, 1});
+		tb.allocateBlock();
+		tb.set(0, 0, 5.244058388023880);
+		// decimal=2 must print exactly two fraction digits, not DecimalFormat's default max of 3
+		String out = DataConverter.toString(tb, false, " ", "\n", "[", "]", 1, 1, 2);
+		assertTrue("expected value clamped to 5.24, got: " + out, out.contains("5.24"));
+		assertFalse("decimal=2 must not print three digits: " + out, out.contains("5.244"));
+	}
+
+	@Test
+	public void testDecimalPadsAndRounds() {
+		TensorBlock tb = new TensorBlock(ValueType.FP64, new int[]{1, 2});
+		tb.allocateBlock();
+		tb.set(0, 0, 22.0);                // integer-valued: padded up to the requested digits
+		tb.set(0, 1, 5.244058388023880);   // rounded at the last requested digit
+		String out = DataConverter.toString(tb, false, " ", "\n", "[", "]", 1, 2, 4);
+		assertTrue("expected 22.0000 padded: " + out, out.contains("22.0000"));
+		assertTrue("expected 5.2441 rounded: " + out, out.contains("5.2441"));
+	}
+
+	@Test
+	public void testNegativeDecimalUsesDefaultFormatting() {
+		TensorBlock tb = new TensorBlock(ValueType.FP64, new int[]{1, 2});
+		tb.allocateBlock();
+		tb.set(0, 0, 22.0);                // integer-valued: no fraction digits when unconstrained
+		tb.set(0, 1, 5.244058388023880);   // default cap of three fraction digits
+		// decimal < 0 leaves DecimalFormat unconstrained (no min/max fraction digits set)
+		String out = DataConverter.toString(tb, false, " ", "\n", "[", "]", 1, 2, -1);
+		assertTrue("expected unpadded 22: " + out, out.contains("22"));
+		assertFalse("integer value must not be padded: " + out, out.contains("22.0"));
+		assertTrue("expected default 5.244: " + out, out.contains("5.244"));
+		assertFalse("must not print a fourth digit: " + out, out.contains("5.2441"));
+	}
+}

src/test/java/org/apache/sysds/test/functions/misc/ToStringTest.java

@@ -270,4 +270,96 @@ protected void toStringTestHelper(ExecMode platform, String testName, String exp
 			DMLScript.USE_LOCAL_SPARK_CONFIG = sparkConfigOld;
 		}
 	}
+
+	@Test
+	public void testPrintWithDecimal(){
+		String testName = "ToString12";
+
+		String decimalPoints = "2";
+		String value = "22";
+		String expectedOutput = "22.00\n";
+
+		addTestConfiguration(testName, new TestConfiguration(TEST_CLASS_DIR, testName));
+		toStringTestHelper2(ExecMode.SINGLE_NODE, testName, expectedOutput, decimalPoints, value);
+	}
+
+
+	@Test
+	public void testPrintWithDecimal2(){
+		String testName = "ToString12";
+
+		String decimalPoints = "2";
+		String value = "5.244058388023880";
+		String expectedOutput = "5.24\n";
+
+		addTestConfiguration(testName, new TestConfiguration(TEST_CLASS_DIR, testName));
+		toStringTestHelper2(ExecMode.SINGLE_NODE, testName, expectedOutput, decimalPoints, value);
+	}
+
+
+	@Test
+	public void testPrintWithDecimal3(){
+		String testName = "ToString12";
+
+		String decimalPoints = "10";
+		String value = "5.244058388023880";
+		String expectedOutput = "5.2440583880\n";
+
+		addTestConfiguration(testName, new TestConfiguration(TEST_CLASS_DIR, testName));
+		toStringTestHelper2(ExecMode.SINGLE_NODE, testName, expectedOutput, decimalPoints, value);
+	}
+
+
+	@Test
+	public void testPrintWithDecimal4(){
+		String testName = "ToString12";
+
+		String decimalPoints = "4";
+		String value = "5.244058388023880";
+		String expectedOutput = "5.2441\n";
+
+		addTestConfiguration(testName, new TestConfiguration(TEST_CLASS_DIR, testName));
+		toStringTestHelper2(ExecMode.SINGLE_NODE, testName, expectedOutput, decimalPoints, value);
+	}
+
+
+	@Test
+	public void testPrintWithDecimal5(){
+		String testName = "ToString12";
+
+		String decimalPoints = "10";
+		String value = "0.000000008023880";
+		String expectedOutput = "0.0000000080\n";
+
+		addTestConfiguration(testName, new TestConfiguration(TEST_CLASS_DIR, testName));
+		toStringTestHelper2(ExecMode.SINGLE_NODE, testName, expectedOutput, decimalPoints, value);
+	}
+
+	protected void toStringTestHelper2(ExecMode platform, String testName, String expectedOutput, String decimalPoints, String value) {
+		ExecMode platformOld = rtplatform;
+
+		rtplatform = platform;
+		boolean sparkConfigOld = DMLScript.USE_LOCAL_SPARK_CONFIG;
+		if (rtplatform == ExecMode.SPARK)
+			DMLScript.USE_LOCAL_SPARK_CONFIG = true;
+		try {
+			// Create and load test configuration
+			getAndLoadTestConfiguration(testName);
+			String HOME = SCRIPT_DIR + TEST_DIR;
+			fullDMLScriptName = HOME + testName + ".dml";
+			programArgs = new String[]{"-args", output(OUTPUT_NAME), value, decimalPoints};
+
+			// Run DML and R scripts
+			runTest(true, false, null, -1);
+
+			// Compare output strings
+			String output = TestUtils.readDMLString(output(OUTPUT_NAME));
+			TestUtils.compareScalars(expectedOutput, output);
+		}
+		finally {
+			// Reset settings
+			rtplatform = platformOld;
+			DMLScript.USE_LOCAL_SPARK_CONFIG = sparkConfigOld;
+		}
+	}
 }

src/test/scripts/functions/misc/ToString12.dml

@@ -0,0 +1,24 @@
+#-------------------------------------------------------------
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+#
+#-------------------------------------------------------------
+
+X = matrix($2, rows=1, cols=1)
+str = toString(X, rows=3, cols=3, decimal=$3)
+write(str, $1)