Fix, document, and test ColumnType.compare and Table.compareRows (#21)

* Fix document and test ColumnType.compare and Table.compareRows

* Fix sonar comment

* More explicit test name

core/src/main/java/tech/tablesaw/api/ColumnType.java

@@ -82,10 +82,17 @@ static ColumnType valueOf(String name) {
   /** TODO: Research this method to provide a good comment */
   AbstractColumnParser<?> customParser(ReadOptions options);
 
-  /** TODO: Research this method to provide a good comment */
-  default boolean compare(int rowNumber, Column<?> temp, Column<?> original) {
-    Object o1 = original.get(rowNumber);
-    Object o2 = temp.get(temp.size() - 1);
+  /**
+   * Compare the row at {@code rownumber} in {@code column1} and {@code column2} and returns whether they are equals.
+   * @param rowNumber the row to compare
+   * @param column1 the first column to compare
+   * @param column2 the second column to compare
+   * @return true if row {@code rownumber} is equals in both columns
+   * @throws {@code IndexOutOfBoundsException} if {@code rownumber} exceeds either column size
+   */
+  default boolean compare(int rowNumber, Column<?> column1, Column<?> column2) {
+    Object o1 = column2.get(rowNumber);
+    Object o2 = column1.get(rowNumber);
     return o1 == null ? o2 == null : o1.equals(o2);
   }
 

core/src/main/java/tech/tablesaw/api/Table.java

@@ -529,17 +529,20 @@ public void copyRowsToTable(int[] rows, Table newTable) {
   }
 
   /**
-   * Returns {@code true} if the row @rowNumber in table1 holds the same data as the row at
-   * rowNumber in table2
+   * Returns {@code true} if the row {@code rowNumber} in {@code table1} holds the same values than the row at
+   * {@code rowNumber} in {@code table2}. Returns false if the number of columns is different in the two tables.
+   * @param rowNumber the row to compare
+   * @param table1 the first table to compare
+   * @param table2 the second table to compare
+   * @return false if row {@code rowNumber} is different in {@code table1} and {@code table2}
+   * @throws {@code IndexOutOfBoundsException} if {@code rownumber} exceeds either table number of rows
    */
   public static boolean compareRows(int rowNumber, Table table1, Table table2) {
-    int columnCount = table1.columnCount();
-    boolean result;
+    final int columnCount = table1.columnCount();
+    if (columnCount != table2.columnCount()) return false;
     for (int columnIndex = 0; columnIndex < columnCount; columnIndex++) {
       ColumnType columnType = table1.column(columnIndex).type();
-      result =
-          columnType.compare(rowNumber, table2.column(columnIndex), table1.column(columnIndex));
-      if (!result) {
+      if (!columnType.compare(rowNumber, table2.column(columnIndex), table1.column(columnIndex))) {
         return false;
       }
     }

core/src/test/java/tech/tablesaw/api/TableCompareRowsTest.java

@@ -0,0 +1,56 @@
+package tech.tablesaw.api;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.io.File;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import tech.tablesaw.io.csv.CsvReadOptions;
+
+class TableCompareRowsTest {
+
+    private static final String SOURCE_FILE_NAME = "../data/missing_values.csv";
+    private static Table testTable;
+
+    @BeforeAll
+    static void readTables() {
+        testTable = Table.read().usingOptions(CsvReadOptions
+            .builder(new File(SOURCE_FILE_NAME))
+            .missingValueIndicator("-"));
+    }
+
+    @Test
+    void testCompareRowsIdentical() {
+        for(int i = 0; i < testTable.rowCount(); i++) {
+            assertTrue(Table.compareRows(i, testTable, testTable), "Row " + i + " is not equal to itself");
+        }
+    }
+
+    @Test
+    void testCompareRowsDifferent() {
+        Table differentTable = testTable.copy().sortDescendingOn("Sales");
+        for(int i = 0; i < testTable.rowCount(); i++) {
+            assertFalse(Table.compareRows(i, testTable, differentTable), "Row " + i + " is equal to a different row");
+        }
+    }
+
+    @Test
+    void testCompareRowsDifferentColumns() {
+        Table differentTable = testTable.copy().removeColumns("Sales");
+        for(int i = 0; i < testTable.rowCount(); i++) {
+            assertFalse(Table.compareRows(i, testTable, differentTable), "Row " + i + " is equal to a row with less columns");
+        }
+    }
+
+    @Test
+    void testCompareRowsOutOfBound() {
+        Table differentTable = testTable.copy().dropRows(0);
+        int lastRowNumber = testTable.rowCount() - 1;
+        assertThrows(IndexOutOfBoundsException.class,
+            () -> Table.compareRows(lastRowNumber, testTable, differentTable),
+            "Row outside range does not throw exception");
+    }
+
+}