Bugzilla 54356: Support of statistical function INTERCEPT

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1426485 13f79535-47bb-0310-9956-ffa450edef68

5 files changed, 386 insertions, 0 deletions

diff --git a/src/documentation/content/xdocs/status.xml b/src/documentation/content/xdocs/status.xml
index 8fef9acb23..2016c13d2d 100644
--- a/src/documentation/content/xdocs/status.xml
+++ b/src/documentation/content/xdocs/status.xml
@@ -34,6 +34,7 @@
 
     <changes>
         <release version="4.0-beta1" date="2013-??-??">
+          <action dev="poi-developers" type="add">54356 - Support for INTERCEPT function</action>
           <action dev="poi-developers" type="fix">54282 - Improve the performance of ColumnHelper addCleanColIntoCols, speeds up some .xlsx file loading</action>
           <action dev="poi-developers" type="fix">53650 - Prevent unreadable content and disalow to overwrite rows from input template in SXSSF</action>
           <action dev="poi-developers" type="fix">54228,53672 - Fixed XSSF to read cells with missing R attribute</action>
diff --git a/src/java/org/apache/poi/ss/formula/eval/FunctionEval.java b/src/java/org/apache/poi/ss/formula/eval/FunctionEval.java
index c76da52c17..021d6980f0 100644
--- a/src/java/org/apache/poi/ss/formula/eval/FunctionEval.java
+++ b/src/java/org/apache/poi/ss/formula/eval/FunctionEval.java
@@ -28,6 +28,7 @@ import java.util.TreeSet;
 
 /**
  * @author Amol S. Deshmukh &lt; amolweb at ya hoo dot com &gt;
+ * @author Johan Karlsteen - added Intercept
  */
 public final class FunctionEval {
 	/**
@@ -208,6 +209,8 @@ public final class FunctionEval {
 		retval[304] = new Sumx2my2();
 		retval[305] = new Sumx2py2();
 
+		retval[311] = new Intercept();
+
 		retval[318] = AggregateFunction.DEVSQ;
 
 		retval[321] = AggregateFunction.SUMSQ;
diff --git a/src/java/org/apache/poi/ss/formula/functions/Intercept.java b/src/java/org/apache/poi/ss/formula/functions/Intercept.java
new file mode 100644
index 0000000000..06bb6f97db
--- /dev/null
+++ b/src/java/org/apache/poi/ss/formula/functions/Intercept.java
@@ -0,0 +1,223 @@
+/*
+ *  ====================================================================
+ *    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.TwoDEval;
+import org.apache.poi.ss.formula.eval.ErrorEval;
+import org.apache.poi.ss.formula.eval.EvaluationException;
+import org.apache.poi.ss.formula.eval.NumberEval;
+import org.apache.poi.ss.formula.eval.RefEval;
+import org.apache.poi.ss.formula.eval.ValueEval;
+import org.apache.poi.ss.formula.functions.LookupUtils.ValueVector;
+
+/**
+ * Implementation of Excel function INTERCEPT()<p/>
+ *
+ * Calculates the INTERCEPT of the linear regression line that is used to predict y values from x values<br/>
+ * (http://introcs.cs.princeton.edu/java/97data/LinearRegression.java.html)
+ * <b>Syntax</b>:<br/>
+ * <b>INTERCEPT</b>(<b>arrayX</b>, <b>arrayY</b>)<p/>
+ *
+ *
+ * @author Johan Karlsteen
+ */
+public final class Intercept extends Fixed2ArgFunction {
+
+	private static abstract class ValueArray implements ValueVector {
+		private final int _size;
+		protected ValueArray(int size) {
+			_size = size;
+		}
+
+		public ValueEval getItem(int index) {
+			if (index < 0 || index > _size) {
+				throw new IllegalArgumentException("Specified index " + index
+						+ " is outside range (0.." + (_size - 1) + ")");
+			}
+			return getItemInternal(index);
+		}
+		protected abstract ValueEval getItemInternal(int index);
+
+		public final int getSize() {
+			return _size;
+		}
+	}
+
+	private static final class SingleCellValueArray extends ValueArray {
+		private final ValueEval _value;
+		public SingleCellValueArray(ValueEval value) {
+			super(1);
+			_value = value;
+		}
+		@Override
+		protected ValueEval getItemInternal(int index) {
+			return _value;
+		}
+	}
+
+	private static final class RefValueArray extends ValueArray {
+		private final RefEval _ref;
+		public RefValueArray(RefEval ref) {
+			super(1);
+			_ref = ref;
+		}
+		@Override
+		protected ValueEval getItemInternal(int index) {
+			return _ref.getInnerValueEval();
+		}
+	}
+
+	private static final class AreaValueArray extends ValueArray {
+		private final TwoDEval _ae;
+		private final int _width;
+
+		public AreaValueArray(TwoDEval ae) {
+			super(ae.getWidth() * ae.getHeight());
+			_ae = ae;
+			_width = ae.getWidth();
+		}
+		@Override
+		protected ValueEval getItemInternal(int index) {
+			int rowIx = index / _width;
+			int colIx = index % _width;
+			return _ae.getValue(rowIx, colIx);
+		}
+	}
+
+	
+	public ValueEval evaluate(int srcRowIndex, int srcColumnIndex,
+			ValueEval arg0, ValueEval arg1) {
+		double result;
+		try {
+			ValueVector vvX = createValueVector(arg0);
+			ValueVector vvY = createValueVector(arg1);
+			int size = vvX.getSize();
+			if (size == 0 || vvY.getSize() != size) {
+				return ErrorEval.NA;
+			}
+			result = evaluateInternal(vvX, vvY, size);
+		} catch (EvaluationException e) {
+			return e.getErrorEval();
+		}
+		if (Double.isNaN(result) || Double.isInfinite(result)) {
+			return ErrorEval.NUM_ERROR;
+		}
+		return new NumberEval(result);
+	}
+	
+	private double evaluateInternal(ValueVector x, ValueVector y, int size)
+			throws EvaluationException {
+
+		// error handling is as if the x is fully evaluated before y
+		ErrorEval firstXerr = null;
+		ErrorEval firstYerr = null;
+		boolean accumlatedSome = false;
+		double result = 0.0;
+        // first pass: read in data, compute xbar and ybar
+        double sumx = 0.0, sumy = 0.0;
+        
+		for (int i = 0; i < size; i++) {
+			ValueEval vx = x.getItem(i);
+			ValueEval vy = y.getItem(i);
+			if (vx instanceof ErrorEval) {
+				if (firstXerr == null) {
+					firstXerr = (ErrorEval) vx;
+					continue;
+				}
+			}
+			if (vy instanceof ErrorEval) {
+				if (firstYerr == null) {
+					firstYerr = (ErrorEval) vy;
+					continue;
+				}
+			}
+			// only count pairs if both elements are numbers
+			if (vx instanceof NumberEval && vy instanceof NumberEval) {
+				accumlatedSome = true;
+				NumberEval nx = (NumberEval) vx;
+				NumberEval ny = (NumberEval) vy;
+				sumx  += nx.getNumberValue();
+	            sumy  += ny.getNumberValue();
+			} else {
+				// all other combinations of value types are silently ignored
+			}
+		}
+		double xbar = sumx / size;
+        double ybar = sumy / size;
+		
+		 // second pass: compute summary statistics
+        double xxbar = 0.0, xybar = 0.0;
+        for (int i = 0; i < size; i++) {
+			ValueEval vx = x.getItem(i);
+			ValueEval vy = y.getItem(i);
+			
+			if (vx instanceof ErrorEval) {
+				if (firstXerr == null) {
+					firstXerr = (ErrorEval) vx;
+					continue;
+				}
+			}
+			if (vy instanceof ErrorEval) {
+				if (firstYerr == null) {
+					firstYerr = (ErrorEval) vy;
+					continue;
+				}
+			}
+			
+			// only count pairs if both elements are numbers
+			if (vx instanceof NumberEval && vy instanceof NumberEval) {
+				NumberEval nx = (NumberEval) vx;
+				NumberEval ny = (NumberEval) vy;
+	            xxbar += (nx.getNumberValue() - xbar) * (nx.getNumberValue() - xbar);
+	            xybar += (nx.getNumberValue() - xbar) * (ny.getNumberValue() - ybar);
+			} else {
+				// all other combinations of value types are silently ignored
+			}
+        }
+        double beta1 = xybar / xxbar;
+        double beta0 = ybar - beta1 * xbar;
+		
+		if (firstXerr != null) {
+			throw new EvaluationException(firstXerr);
+		}
+		if (firstYerr != null) {
+			throw new EvaluationException(firstYerr);
+		}
+		if (!accumlatedSome) {
+			throw new EvaluationException(ErrorEval.DIV_ZERO);
+		}
+		
+		result = beta0;
+		return result;
+	}
+
+	private static ValueVector createValueVector(ValueEval arg) throws EvaluationException {
+		if (arg instanceof ErrorEval) {
+			throw new EvaluationException((ErrorEval) arg);
+		}
+		if (arg instanceof TwoDEval) {
+			return new AreaValueArray((TwoDEval) arg);
+		}
+		if (arg instanceof RefEval) {
+			return new RefValueArray((RefEval) arg);
+		}
+		return new SingleCellValueArray(arg);
+	}
+}
\ No newline at end of file
diff --git a/src/testcases/org/apache/poi/ss/formula/functions/TestIntercept.java b/src/testcases/org/apache/poi/ss/formula/functions/TestIntercept.java
new file mode 100644
index 0000000000..942ab6b019
--- /dev/null
+++ b/src/testcases/org/apache/poi/ss/formula/functions/TestIntercept.java
@@ -0,0 +1,159 @@
+/*
+ *  ====================================================================
+ *    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 junit.framework.TestCase;
+
+import org.apache.poi.hssf.HSSFTestDataSamples;
+import org.apache.poi.hssf.usermodel.HSSFCell;
+import org.apache.poi.hssf.usermodel.HSSFFormulaEvaluator;
+import org.apache.poi.hssf.usermodel.HSSFSheet;
+import org.apache.poi.hssf.usermodel.HSSFWorkbook;
+import org.apache.poi.ss.formula.eval.ErrorEval;
+import org.apache.poi.ss.formula.eval.NumberEval;
+import org.apache.poi.ss.formula.eval.ValueEval;
+/**
+ * Test for Excel function INTERCEPT()
+ *
+ * @author Johan Karlsteen
+ */
+public final class TestIntercept extends TestCase {
+	private static final Function INTERCEPT = new Intercept();
+
+	private static ValueEval invoke(Function function, ValueEval xArray, ValueEval yArray) {
+		ValueEval[] args = new ValueEval[] { xArray, yArray, };
+		return function.evaluate(args, -1, (short)-1);
+	}
+
+	private void confirm(Function function, ValueEval xArray, ValueEval yArray, double expected) {
+		ValueEval result = invoke(function, xArray, yArray);
+		assertEquals(NumberEval.class, result.getClass());
+		assertEquals(expected, ((NumberEval)result).getNumberValue(), 0);
+	}
+	private void confirmError(Function function, ValueEval xArray, ValueEval yArray, ErrorEval expectedError) {
+		ValueEval result = invoke(function, xArray, yArray);
+		assertEquals(ErrorEval.class, result.getClass());
+		assertEquals(expectedError.getErrorCode(), ((ErrorEval)result).getErrorCode());
+	}
+
+	private void confirmError(ValueEval xArray, ValueEval yArray, ErrorEval expectedError) {
+		confirmError(INTERCEPT, xArray, yArray, expectedError);
+	}
+
+	public void testBasic() {
+		Double exp = Math.pow(10, 7.5);
+		ValueEval[] xValues = {
+			new NumberEval(3+exp),
+			new NumberEval(4+exp),
+			new NumberEval(2+exp),
+			new NumberEval(5+exp),
+			new NumberEval(4+exp),
+			new NumberEval(7+exp),
+		};
+		ValueEval areaEvalX = createAreaEval(xValues);
+
+		ValueEval[] yValues = {
+			new NumberEval(1),
+			new NumberEval(2),
+			new NumberEval(3),
+			new NumberEval(4),
+			new NumberEval(5),
+			new NumberEval(6),
+		};
+		ValueEval areaEvalY = createAreaEval(yValues);
+		confirm(INTERCEPT, areaEvalX, areaEvalY, -24516534.39905822);
+		// Excel 2010 gives -24516534.3990583
+	}
+
+	/**
+	 * number of items in array is not limited to 30
+	 */
+	public void testLargeArrays() {
+		ValueEval[] xValues = createMockNumberArray(100, 3); // [1,2,0,1,2,0,...,0,1]
+		xValues[0] = new NumberEval(2.0); // Changes first element to 2
+		ValueEval[] yValues = createMockNumberArray(100, 101); // [1,2,3,4,...,99,100]
+
+		confirm(INTERCEPT, createAreaEval(xValues), createAreaEval(yValues), 51.74384236453202);
+		// Excel 2010 gives 51.74384236453200
+	}
+
+	private ValueEval[] createMockNumberArray(int size, double value) {
+		ValueEval[] result = new ValueEval[size];
+		for (int i = 0; i < result.length; i++) {
+			result[i] = new NumberEval((i+1)%value);
+		}
+		return result;
+	}
+
+	private static ValueEval createAreaEval(ValueEval[] values) {
+		String refStr = "A1:A" + values.length;
+		return EvalFactory.createAreaEval(refStr, values);
+	}
+
+	public void testErrors() {
+		ValueEval[] xValues = {
+				ErrorEval.REF_INVALID,
+				new NumberEval(2),
+		};
+		ValueEval areaEvalX = createAreaEval(xValues);
+		ValueEval[] yValues = {
+				new NumberEval(2),
+				ErrorEval.NULL_INTERSECTION,
+		};
+		ValueEval areaEvalY = createAreaEval(yValues);
+		ValueEval[] zValues = { // wrong size
+				new NumberEval(2),
+		};
+		ValueEval areaEvalZ = createAreaEval(zValues);
+
+		// if either arg is an error, that error propagates
+		confirmError(ErrorEval.REF_INVALID, ErrorEval.NAME_INVALID, ErrorEval.REF_INVALID);
+		confirmError(areaEvalX, ErrorEval.NAME_INVALID, ErrorEval.NAME_INVALID);
+		confirmError(ErrorEval.NAME_INVALID, areaEvalX, ErrorEval.NAME_INVALID);
+
+		// array sizes must match
+		confirmError(areaEvalX, areaEvalZ, ErrorEval.NA);
+		confirmError(areaEvalZ, areaEvalY, ErrorEval.NA);
+
+		// any error in an array item propagates up
+		confirmError(areaEvalX, areaEvalX, ErrorEval.REF_INVALID);
+
+		// search for errors array by array, not pair by pair
+		confirmError(areaEvalX, areaEvalY, ErrorEval.REF_INVALID);
+		confirmError(areaEvalY, areaEvalX, ErrorEval.NULL_INTERSECTION);
+	}
+
+    /**
+     *  Example from
+     *  http://office.microsoft.com/en-us/excel-help/intercept-function-HP010062512.aspx?CTT=5&origin=HA010277524
+     */
+    public void testFromFile() {
+
+        HSSFWorkbook wb = HSSFTestDataSamples.openSampleWorkbook("intercept.xls");
+        HSSFFormulaEvaluator fe = new HSSFFormulaEvaluator(wb);
+
+        HSSFSheet example1 = wb.getSheet("Example 1");
+        HSSFCell a8 = example1.getRow(7).getCell(0);
+        assertEquals("INTERCEPT(A2:A6,B2:B6)", a8.getCellFormula());
+        fe.evaluate(a8);
+        assertEquals(0.048387097, a8.getNumericCellValue(), 0.000000001);
+
+    }
+}
\ No newline at end of file
diff --git a/test-data/spreadsheet/intercept.xls b/test-data/spreadsheet/intercept.xls
new file mode 100644
index 0000000000..b734887c39
--- /dev/null
+++ b/test-data/spreadsheet/intercept.xls