GroupBy.rowNumber() #16

* adding Series.concat functionality to concatenate series

dflib/src/main/java/com/nhl/dflib/Series.java

@@ -1,5 +1,6 @@
 package com.nhl.dflib;
 
+import com.nhl.dflib.concat.SeriesConcat;
 import com.nhl.dflib.series.ArraySeries;
 import com.nhl.dflib.series.EmptySeries;
 import com.nhl.dflib.series.RangeSeries;
@@ -42,4 +43,16 @@ default Series<T> openClosedRange(int fromInclusive, int toExclusive) {
     Series<T> fillNullsBackwards();
 
     Series<T> fillNullsForward();
+
+    default Series<T> concat(Series<? extends T>... other) {
+        if (other.length == 0) {
+            return this;
+        }
+
+        Series<? extends T>[] combined = new Series[other.length + 1];
+        combined[0] = this;
+        System.arraycopy(other, 0, combined, 1, other.length);
+
+        return SeriesConcat.concat(combined);
+    }
 }

dflib/src/main/java/com/nhl/dflib/concat/SeriesConcat.java

@@ -0,0 +1,25 @@
+package com.nhl.dflib.concat;
+
+import com.nhl.dflib.Series;
+import com.nhl.dflib.series.ArraySeries;
+
+public class SeriesConcat {
+
+    public static <T> Series<T> concat(Series<? extends T>... concat) {
+
+        int h = 0;
+        int n = concat.length;
+        for (Series<?> s : concat) {
+            h += s.size();
+        }
+
+        T[] data = (T[]) new Object[h];
+        for (int i = 0, ai = 0; i < n; i++) {
+            int len = concat[i].size();
+            concat[i].copyTo(data, 0, ai, len);
+            ai += len;
+        }
+
+        return new ArraySeries<>(data);
+    }
+}

dflib/src/test/java/com/nhl/dflib/Series_ConcatTest.java

@@ -0,0 +1,47 @@
+package com.nhl.dflib;
+
+import com.nhl.dflib.unit.SeriesAsserts;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+
+import java.util.Collection;
+
+import static org.junit.Assert.*;
+
+@RunWith(Parameterized.class)
+public class Series_ConcatTest extends BaseSeriesTest {
+
+    public Series_ConcatTest(SeriesTypes seriesType) {
+        super(seriesType);
+    }
+
+    @Parameterized.Parameters
+    public static Collection<Object[]> data() {
+        return ALL_SERIES_TYPES;
+    }
+
+    @Test
+    public void testConcat_None() {
+        Series<String> s = createSeries("a", "b");
+        assertSame(s, s.concat());
+    }
+
+    @Test
+    public void testConcat_Self() {
+        Series<String> s = createSeries("a", "b");
+        Series<String> c = s.concat(s);
+        new SeriesAsserts(c).expectData("a", "b", "a", "b");
+    }
+
+    @Test
+    public void testConcat() {
+        Series<String> s1 = createSeries("m", "n");
+        Series<String> s2 = createSeries("a", "b");
+        Series<String> s3 = createSeries("d", "c");
+
+        Series<String> c = s1.concat(s2, s3);
+        new SeriesAsserts(c).expectData("m", "n", "a", "b", "d", "c");
+    }
+}
+