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 8442f5832f..961a9cd81c 100644
--- a/src/java/org/apache/poi/ss/formula/eval/FunctionEval.java
+++ b/src/java/org/apache/poi/ss/formula/eval/FunctionEval.java
@@ -115,7 +115,7 @@ public final class FunctionEval {
// 47: DVAR
retval[48] = TextFunction.TEXT;
// 49: LINEST
- // 50: TREND
+ retval[50] = new Trend();
// 51: LOGEST
// 52: GROWTH
diff --git a/src/java/org/apache/poi/ss/formula/functions/Trend.java b/src/java/org/apache/poi/ss/formula/functions/Trend.java
new file mode 100644
index 0000000000..155c1a57a5
--- /dev/null
+++ b/src/java/org/apache/poi/ss/formula/functions/Trend.java
@@ -0,0 +1,377 @@
+/* ====================================================================
+ 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.
+==================================================================== */
+
+/*
+ * Notes:
+ * Duplicate x values don't work most of the time because of the way the
+ * math library handles multiple regression.
+ * The math library currently fails when the number of x variables is >=
+ * the sample size (see https://github.com/Hipparchus-Math/hipparchus/issues/13).
+ */
+
+package org.apache.poi.ss.formula.functions;
+
+import org.apache.poi.ss.formula.CacheAreaEval;
+import org.apache.poi.ss.formula.eval.AreaEval;
+import org.apache.poi.ss.formula.eval.BoolEval;
+import org.apache.poi.ss.formula.eval.ErrorEval;
+import org.apache.poi.ss.formula.eval.EvaluationException;
+import org.apache.poi.ss.formula.eval.MissingArgEval;
+import org.apache.poi.ss.formula.eval.NotImplementedException;
+import org.apache.poi.ss.formula.eval.NumberEval;
+import org.apache.poi.ss.formula.eval.NumericValueEval;
+import org.apache.poi.ss.formula.eval.RefEval;
+import org.apache.poi.ss.formula.eval.ValueEval;
+import org.apache.commons.math3.linear.SingularMatrixException;
+import org.apache.commons.math3.stat.regression.OLSMultipleLinearRegression;
+
+import java.util.Arrays;
+
+
+/**
+ * Implementation for the Excel function TREND
+ *
+ * Syntax:
+ * TREND(known_y's, known_x's, new_x's, constant)
+ *
+ * | known_y's, known_x's, new_x's | typically area references, possibly cell references or scalar values |
|---|
+ * | constant | TRUE or FALSE:
+ * determines whether the regression line should include an intercept term |
|---|
+ *
+ * If known_x's is not given, it is assumed to be the default array {1, 2, 3, ...}
+ * of the same size as known_y's.
+ * If new_x's is not given, it is assumed to be the same as known_x's
+ * If constant is omitted, it is assumed to be TRUE
+ *
+ */
+
+public final class Trend implements Function {
+ MatrixFunction.MutableValueCollector collector = new MatrixFunction.MutableValueCollector(false, false);
+ private static final class TrendResults {
+ public double[] vals;
+ public int resultWidth;
+ public int resultHeight;
+
+ public TrendResults(double[] vals, int resultWidth, int resultHeight) {
+ this.vals = vals;
+ this.resultWidth = resultWidth;
+ this.resultHeight = resultHeight;
+ }
+ }
+
+ public ValueEval evaluate(ValueEval[] args, int srcRowIndex, int srcColumnIndex) {
+ if (args.length < 1 || args.length > 4) {
+ return ErrorEval.VALUE_INVALID;
+ }
+ try {
+ TrendResults tr = getNewY(args);
+ ValueEval[] vals = new ValueEval[tr.vals.length];
+ for (int i = 0; i < tr.vals.length; i++) {
+ vals[i] = new NumberEval(tr.vals[i]);
+ }
+ if (tr.vals.length == 1) {
+ return vals[0];
+ }
+ return new CacheAreaEval(srcRowIndex, srcColumnIndex, srcRowIndex + tr.resultHeight - 1, srcColumnIndex + tr.resultWidth - 1, vals);
+ } catch (EvaluationException e) {
+ return e.getErrorEval();
+ }
+ }
+
+ private static double[][] evalToArray(ValueEval arg) throws EvaluationException {
+ double[][] ar;
+ ValueEval eval;
+ if (arg instanceof MissingArgEval) {
+ return new double[0][0];
+ }
+ if (arg instanceof RefEval) {
+ RefEval re = (RefEval) arg;
+ if (re.getNumberOfSheets() > 1) {
+ throw new EvaluationException(ErrorEval.VALUE_INVALID);
+ }
+ eval = re.getInnerValueEval(re.getFirstSheetIndex());
+ } else {
+ eval = arg;
+ }
+ if (eval == null) {
+ throw new RuntimeException("Parameter may not be null.");
+ }
+
+ if (eval instanceof AreaEval) {
+ AreaEval ae = (AreaEval) eval;
+ int w = ae.getWidth();
+ int h = ae.getHeight();
+ ar = new double[h][w];
+ for (int i = 0; i < h; i++) {
+ for (int j = 0; j < w; j++) {
+ ValueEval ve = ae.getRelativeValue(i, j);
+ if (!(ve instanceof NumericValueEval)) {
+ throw new EvaluationException(ErrorEval.VALUE_INVALID);
+ }
+ ar[i][j] = ((NumericValueEval)ve).getNumberValue();
+ }
+ }
+ } else if (eval instanceof NumericValueEval) {
+ ar = new double[1][1];
+ ar[0][0] = ((NumericValueEval)eval).getNumberValue();
+ } else {
+ throw new EvaluationException(ErrorEval.VALUE_INVALID);
+ }
+
+ return ar;
+ }
+
+ private static double[][] getDefaultArrayOneD(int w) {
+ double[][] array = new double[w][1];
+ for (int i = 0; i < w; i++) {
+ array[i][0] = i + 1;
+ }
+ return array;
+ }
+
+ private static double[] flattenArray(double[][] twoD) {
+ if (twoD.length < 1) {
+ return new double[0];
+ }
+ double[] oneD = new double[twoD.length * twoD[0].length];
+ for (int i = 0; i < twoD.length; i++) {
+ for (int j = 0; j < twoD[0].length; j++) {
+ oneD[i * twoD[0].length + j] = twoD[i][j];
+ }
+ }
+ return oneD;
+ }
+
+ private static double[][] flattenArrayToRow(double[][] twoD) {
+ if (twoD.length < 1) {
+ return new double[0][0];
+ }
+ double[][] oneD = new double[twoD.length * twoD[0].length][1];
+ for (int i = 0; i < twoD.length; i++) {
+ for (int j = 0; j < twoD[0].length; j++) {
+ oneD[i * twoD[0].length + j][0] = twoD[i][j];
+ }
+ }
+ return oneD;
+ }
+
+ private static double[][] switchRowsColumns(double[][] array) {
+ double[][] newArray = new double[array[0].length][array.length];
+ for (int i = 0; i < array.length; i++) {
+ for (int j = 0; j < array[0].length; j++) {
+ newArray[j][i] = array[i][j];
+ }
+ }
+ return newArray;
+ }
+
+ /**
+ * Check if all columns in a matrix contain the same values.
+ * Return true if the number of distinct values in each column is 1.
+ *
+ * @param matrix column-oriented matrix. A Row matrix should be transposed to column .
+ * @return true if all columns contain the same value
+ */
+ private static boolean isAllColumnsSame(double[][] matrix){
+ if(matrix.length == 0) return false;
+
+ boolean[] cols = new boolean[matrix[0].length];
+ for (int j = 0; j < matrix[0].length; j++) {
+ double prev = Double.NaN;
+ for (int i = 0; i < matrix.length; i++) {
+ double v = matrix[i][j];
+ if(i > 0 && v != prev) {
+ cols[j] = true;
+ break;
+ }
+ prev = v;
+ }
+ }
+ boolean allEquals = true;
+ for (boolean x : cols) {
+ if(x) {
+ allEquals = false;
+ break;
+ }
+ };
+ return allEquals;
+
+ }
+
+ private static TrendResults getNewY(ValueEval[] args) throws EvaluationException {
+ double[][] xOrig;
+ double[][] x;
+ double[][] yOrig;
+ double[] y;
+ double[][] newXOrig;
+ double[][] newX;
+ double[][] resultSize;
+ boolean passThroughOrigin = false;
+ switch (args.length) {
+ case 1:
+ yOrig = evalToArray(args[0]);
+ xOrig = new double[0][0];
+ newXOrig = new double[0][0];
+ break;
+ case 2:
+ yOrig = evalToArray(args[0]);
+ xOrig = evalToArray(args[1]);
+ newXOrig = new double[0][0];
+ break;
+ case 3:
+ yOrig = evalToArray(args[0]);
+ xOrig = evalToArray(args[1]);
+ newXOrig = evalToArray(args[2]);
+ break;
+ case 4:
+ yOrig = evalToArray(args[0]);
+ xOrig = evalToArray(args[1]);
+ newXOrig = evalToArray(args[2]);
+ if (!(args[3] instanceof BoolEval)) {
+ throw new EvaluationException(ErrorEval.VALUE_INVALID);
+ }
+ // The argument in Excel is false when it *should* pass through the origin.
+ passThroughOrigin = !((BoolEval)args[3]).getBooleanValue();
+ break;
+ default:
+ throw new EvaluationException(ErrorEval.VALUE_INVALID);
+ }
+
+ if (yOrig.length < 1) {
+ throw new EvaluationException(ErrorEval.VALUE_INVALID);
+ }
+ y = flattenArray(yOrig);
+ newX = newXOrig;
+
+ if (newXOrig.length > 0) {
+ resultSize = newXOrig;
+ } else {
+ resultSize = new double[1][1];
+ }
+
+ if (y.length == 1) {
+ /* See comment at top of file
+ if (xOrig.length > 0 && !(xOrig.length == 1 || xOrig[0].length == 1)) {
+ throw new EvaluationException(ErrorEval.REF_INVALID);
+ } else if (xOrig.length < 1) {
+ x = new double[1][1];
+ x[0][0] = 1;
+ } else {
+ x = new double[1][];
+ x[0] = flattenArray(xOrig);
+ if (newXOrig.length < 1) {
+ resultSize = xOrig;
+ }
+ }*/
+ throw new NotImplementedException("Sample size too small");
+ } else if (yOrig.length == 1 || yOrig[0].length == 1) {
+ if (xOrig.length < 1) {
+ x = getDefaultArrayOneD(y.length);
+ if (newXOrig.length < 1) {
+ resultSize = yOrig;
+ }
+ } else {
+ x = xOrig;
+ if (xOrig[0].length > 1 && yOrig.length == 1) {
+ x = switchRowsColumns(x);
+ }
+ if (newXOrig.length < 1) {
+ resultSize = xOrig;
+ }
+ }
+ if (newXOrig.length > 0 && (x.length == 1 || x[0].length == 1)) {
+ newX = flattenArrayToRow(newXOrig);
+ }
+ } else {
+ if (xOrig.length < 1) {
+ x = getDefaultArrayOneD(y.length);
+ if (newXOrig.length < 1) {
+ resultSize = yOrig;
+ }
+ } else {
+ x = flattenArrayToRow(xOrig);
+ if (newXOrig.length < 1) {
+ resultSize = xOrig;
+ }
+ }
+ if (newXOrig.length > 0) {
+ newX = flattenArrayToRow(newXOrig);
+ }
+ if (y.length != x.length || yOrig.length != xOrig.length) {
+ throw new EvaluationException(ErrorEval.REF_INVALID);
+ }
+ }
+
+ if (newXOrig.length < 1) {
+ newX = x;
+ } else if (newXOrig.length == 1 && newXOrig[0].length > 1 && xOrig.length > 1 && xOrig[0].length == 1) {
+ newX = switchRowsColumns(newXOrig);
+ }
+
+ if (newX[0].length != x[0].length) {
+ throw new EvaluationException(ErrorEval.REF_INVALID);
+ }
+
+ if (x[0].length >= x.length) {
+ /* See comment at top of file */
+ throw new NotImplementedException("Sample size too small");
+ }
+
+ int resultHeight = resultSize.length;
+ int resultWidth = resultSize[0].length;
+
+ if(isAllColumnsSame(x)){
+ double[] result = new double[newX.length];
+ double avg = Arrays.stream(y).average().orElse(0);
+ for(int i = 0; i < result.length; i++) result[i] = avg;
+ return new TrendResults(result, resultWidth, resultHeight);
+ }
+
+ OLSMultipleLinearRegression reg = new OLSMultipleLinearRegression();
+ if (passThroughOrigin) {
+ reg.setNoIntercept(true);
+ }
+
+ try {
+ reg.newSampleData(y, x);
+ } catch (IllegalArgumentException e) {
+ throw new EvaluationException(ErrorEval.REF_INVALID);
+ }
+ double[] par;
+ try {
+ par = reg.estimateRegressionParameters();
+ } catch (SingularMatrixException e) {
+ throw new NotImplementedException("Singular matrix in input");
+ }
+
+ double[] result = new double[newX.length];
+ for (int i = 0; i < newX.length; i++) {
+ result[i] = 0;
+ if (passThroughOrigin) {
+ for (int j = 0; j < par.length; j++) {
+ result[i] += par[j] * newX[i][j];
+ }
+ } else {
+ result[i] = par[0];
+ for (int j = 1; j < par.length; j++) {
+ result[i] += par[j] * newX[i][j - 1];
+ }
+ }
+ }
+ return new TrendResults(result, resultWidth, resultHeight);
+ }
+}
diff --git a/src/testcases/org/apache/poi/ss/formula/functions/AllSpreadsheetBasedTests.java b/src/testcases/org/apache/poi/ss/formula/functions/AllSpreadsheetBasedTests.java
index 2b34dcf8a4..0dc5ed9233 100644
--- a/src/testcases/org/apache/poi/ss/formula/functions/AllSpreadsheetBasedTests.java
+++ b/src/testcases/org/apache/poi/ss/formula/functions/AllSpreadsheetBasedTests.java
@@ -41,6 +41,7 @@ import org.junit.runners.Suite;
TestQuotientFunctionsFromSpreadsheet.class,
TestReptFunctionsFromSpreadsheet.class,
TestRomanFunctionsFromSpreadsheet.class,
+ TestTrendFunctionsFromSpreadsheet.class,
TestWeekNumFunctionsFromSpreadsheet.class,
TestWeekNumFunctionsFromSpreadsheet2013.class
})
diff --git a/src/testcases/org/apache/poi/ss/formula/functions/TestTrendFunctionsFromSpreadsheet.java b/src/testcases/org/apache/poi/ss/formula/functions/TestTrendFunctionsFromSpreadsheet.java
new file mode 100644
index 0000000000..51871d16e5
--- /dev/null
+++ b/src/testcases/org/apache/poi/ss/formula/functions/TestTrendFunctionsFromSpreadsheet.java
@@ -0,0 +1,31 @@
+/* ====================================================================
+ 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 java.util.Collection;
+
+import org.junit.runners.Parameterized.Parameters;
+
+/**
+* Tests TREND() as loaded from a test data spreadsheet.
+*/
+public class TestTrendFunctionsFromSpreadsheet extends BaseTestFunctionsFromSpreadsheet {
+ @Parameters(name="{0}")
+ public static Collection data() throws Exception {
+ return data(TestTrendFunctionsFromSpreadsheet.class, "Trend.xls");
+ }
+}
diff --git a/test-data/spreadsheet/Trend.xls b/test-data/spreadsheet/Trend.xls
new file mode 100644
index 0000000000..8a88709363
Binary files /dev/null and b/test-data/spreadsheet/Trend.xls differ