Bug 62373: Support for FREQUENCY function

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1844238 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/poi/ss/formula/eval/FunctionEval.java

@@ -243,7 +243,8 @@ public final class FunctionEval {
 
         // 247: DB
         // 252: FEQUENCY
-        
+        retval[252] = Frequency.instance;
+
         retval[FunctionID.EXTERNAL_FUNC] = null; // ExternalFunction is a FreeRefFunction, nominally 255
 
         retval[261] = new Errortype();

src/java/org/apache/poi/ss/formula/functions/Frequency.java

@@ -0,0 +1,81 @@
+/* ====================================================================
+   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.poi.ss.formula.functions;
+
+import org.apache.poi.ss.formula.CacheAreaEval;
+import org.apache.poi.ss.formula.eval.EvaluationException;
+import org.apache.poi.ss.formula.eval.NumberEval;
+import org.apache.poi.ss.formula.eval.ValueEval;
+
+import java.util.Arrays;
+
+/**
+ * Implementation of Excel 'Analysis ToolPak' function FREQUENCY()<br>
+ * Returns a frequency distribution as a vertical array<p>
+ * <p>
+ * <b>Syntax</b><br>
+ * <b>FREQUENCY</b>(<b>data_array</b>, <b>bins_array</b>)<p>
+ * <p>
+ * <b>data_array</b> Required. An array of or reference to a set of values for which you want to count frequencies.
+ * If data_array contains no values, FREQUENCY returns an array of zeros.<br>
+ * <b>bins_array</b> Required. An array of or reference to intervals into which you want to group the values in data_array.
+ * If bins_array contains no values, FREQUENCY returns the number of elements in data_array.<br>
+ *
+ * @author Yegor Kozlov
+ */
+public class Frequency extends Fixed2ArgFunction {
+    public static final Function instance = new Frequency();
+
+    private Frequency() {
+        // enforce singleton
+    }
+
+    public ValueEval evaluate(int srcRowIndex, int srcColumnIndex, ValueEval arg0, ValueEval arg1) {
+        MatrixFunction.MutableValueCollector collector = new MatrixFunction.MutableValueCollector(false, false);
+
+        double[] values;
+        double[] bins;
+        try {
+            values = collector.collectValues(arg0);
+            bins = collector.collectValues(arg1);
+        } catch (EvaluationException e) {
+            return e.getErrorEval();
+        }
+
+        // can bins be not sorted?
+        //bins = Arrays.stream(bins).sorted().distinct().toArray();
+
+        int[] histogram = histogram(values, bins);
+        NumberEval[] result = Arrays.stream(histogram).boxed().map(NumberEval::new).toArray(NumberEval[]::new);
+        return new CacheAreaEval(srcRowIndex, srcColumnIndex,
+                srcRowIndex + result.length - 1, srcColumnIndex, result);
+    }
+
+    static int findBin(double value, double[] bins) {
+        int idx = Arrays.binarySearch(bins, value);
+        return idx >= 0 ? idx + 1 : -idx;
+    }
+
+    static int[] histogram(double[] values, double[] bins) {
+        int[] histogram = new int[bins.length + 1];
+        for (double val : values) {
+            histogram[findBin(val, bins) - 1]++;
+        }
+        return histogram;
+    }
+}

src/testcases/org/apache/poi/ss/formula/functions/TestFrequency.java

@@ -0,0 +1,91 @@
+/* ====================================================================
+   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.poi.ss.formula.functions;
+
+import org.apache.poi.hssf.usermodel.HSSFWorkbook;
+import org.apache.poi.ss.usermodel.*;
+import org.apache.poi.ss.util.CellRangeAddress;
+import org.junit.Test;
+
+import static org.apache.poi.ss.formula.functions.Frequency.histogram;
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Testcase for the function FREQUENCY(data, bins)
+ *
+ * @author Yegor Kozlov
+ */
+public class TestFrequency {
+
+    @Test
+    public void testHistogram() {
+        assertArrayEquals(new int[]{3, 2, 2, 0, 1, 1},
+                histogram(
+                        new double[]{11, 12, 13, 21, 29, 36, 40, 58, 69},
+                        new double[]{20, 30, 40, 50, 60})
+        );
+
+        assertArrayEquals(new int[]{1, 1, 1, 1, 1, 0},
+                histogram(
+                        new double[]{20, 30, 40, 50, 60},
+                        new double[]{20, 30, 40, 50, 60})
+
+        );
+
+        assertArrayEquals(new int[]{2, 3},
+                histogram(
+                        new double[]{20, 30, 40, 50, 60},
+                        new double[]{30})
+
+        );
+    }
+
+    @Test
+    public void testEvaluate() {
+        Workbook wb = new HSSFWorkbook();
+        FormulaEvaluator evaluator = wb.getCreationHelper().createFormulaEvaluator();
+
+        int[] data = {1, 1, 2, 3, 4, 4, 5, 7, 8, 9, 9, 11, 3, 5, 8};
+        int[] bins = {3, 6, 9};
+        Sheet sheet = wb.createSheet();
+        Row dataRow = sheet.createRow(0); // A1:O1
+        for (int i = 0; i < data.length; i++) {
+            dataRow.createCell(i).setCellValue(data[i]);
+        }
+        Row binsRow = sheet.createRow(1);
+        for (int i = 0; i < bins.length; i++) { // A2:C2
+            binsRow.createCell(i).setCellValue(bins[i]);
+        }
+        Row fmlaRow = sheet.createRow(2);
+        CellRange<? extends Cell> arrayFmla = sheet.setArrayFormula("FREQUENCY(A1:O1,A2:C2)", CellRangeAddress.valueOf("A3:A6"));
+        Cell b3 = fmlaRow.createCell(1); // B3
+        b3.setCellFormula("COUNT(FREQUENCY(A1:O1,A2:C2))"); // frequency returns a vertical array of bins+1
+
+        Cell c3 = fmlaRow.createCell(2);
+        c3.setCellFormula("SUM(FREQUENCY(A1:O1,A2:C2))"); // sum of the frequency bins should add up to the number of data values
+
+        assertEquals(5, (int) evaluator.evaluate(arrayFmla.getFlattenedCells()[0]).getNumberValue());
+        assertEquals(4, (int) evaluator.evaluate(arrayFmla.getFlattenedCells()[1]).getNumberValue());
+        assertEquals(5, (int) evaluator.evaluate(arrayFmla.getFlattenedCells()[2]).getNumberValue());
+        assertEquals(1, (int) evaluator.evaluate(arrayFmla.getFlattenedCells()[3]).getNumberValue());
+
+        assertEquals(4, (int) evaluator.evaluate(b3).getNumberValue());
+        assertEquals(15, (int) evaluator.evaluate(c3).getNumberValue());
+
+    }
+}