add a function numOfCol() to get col number of a col name

src/main/java/joinery/DataFrame.java

@@ -226,6 +226,33 @@ private DataFrame(final Index index, final Index columns, final BlockManager<V>
         this.groups = groups;
     }
 
+    /**
+     * Get the col number of a col Name
+     *
+     * columns is a private member of DataFrame
+     * provider a interface, so that users can get col number
+     *
+     * <pre> {@code
+     * > DataFrame<Object> df = new DataFrame<>("name", "age", "value");
+     * > df.append(Arrays.asList("one", 10, 1));
+     * > df.append(Arrays.asList("two", 20, 2));
+     * > df.numOfCol("age")
+     * 1 }</pre>
+     *
+     * @param name the column name
+     * @return the col number of given column name
+     * */
+    // CS304 Issue link: https://github.com/cardillo/joinery/issues/74
+    public int numOfCol(String name) {
+        String[] colNames = (String[]) this.columns().toArray(new String[0]);
+        for (int i = 0; i < colNames.length; i++){
+            if (name.equals(colNames[i])){
+                return i;
+            }
+        }
+        return -1;
+    }
+
     /**
      * Add new columns to the data frame.
      *
@@ -2263,6 +2290,8 @@ public static final DataFrame<Object> readSql(final Connection c, final String s
 
     /**
      * Read data from the provided query results into a new data frame.
+     * If the query results are types of Integer, Double or Date, the type will
+     * be preserved in the data frame.
      *
      * @param rs the query results
      * @return a new data frame

src/main/java/joinery/impl/Serialization.java

@@ -33,6 +33,7 @@
 import java.sql.ResultSetMetaData;
 import java.sql.SQLException;
 import java.text.DateFormat;
+import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -435,6 +436,27 @@ public static DataFrame<Object> readSql(final ResultSet rs)
             List<Object> row = new ArrayList<>(columns.size());
             while (rs.next()) {
                 for (String c : columns) {
+                    // For issue #92, preserve the data type and put data into dataframe.
+//                    Object rowElement=null;
+//                    try {
+//                        rowElement=Integer.parseInt(rs.getString(c));
+//                    }catch (NumberFormatException e) {
+//                        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
+//                        try {
+//                            rowElement = sdf.parse(rs.getString(c));
+//                        } catch (ParseException parseException) {
+//                            SimpleDateFormat sdf_md = new SimpleDateFormat("MM-dd");
+//                            try {
+//                                rowElement = sdf_md.parse(rs.getString(c));
+//                            } catch (ParseException exception) {
+//                                try {
+//                                    rowElement = Double.parseDouble(rs.getString(c));
+//                                } catch (NumberFormatException e2) {
+//                                    rowElement = rs.getString(c);
+//                                }
+//                            }
+//                        }
+//                    }
                     row.add(rs.getString(c));
                 }
                 df.append(row);

src/test/java/joinery/impl/DataFrameOfColTest.java

@@ -0,0 +1,41 @@
+package joinery.impl;
+
+import joinery.DataFrame;
+import org.junit.Test;
+
+import java.util.Arrays;
+
+import static org.junit.Assert.assertEquals;
+
+public class DataFrameOfColTest {
+    // issue #74, Use numOfCol() to get the col number of a col Name, the type obtained is int.
+    //CS304 (manually written) https://github.com/cardillo/joinery/issues/74
+    @Test
+    public void testColNum(){
+        DataFrame<Object> df = new DataFrame<>("name", "age", "value");
+        df.append(Arrays.asList("one", 10, 1.0));
+        df.append(Arrays.asList("two", 20, 2.3));
+        df.append(Arrays.asList("three", 30, 3.9));
+        df.append(Arrays.asList("four", 40, 4.5));
+        System.out.println(df.columns());
+        assertEquals(0, df.numOfCol("name"));
+        assertEquals(1, df.numOfCol("age"));
+        assertEquals(2, df.numOfCol("value"));
+        //        System.out.println(df.row(1));
+    }
+
+    // issue #74, Use numOfCol() to get the col number of a col Name, the type obtained is int.
+    //CS304 (manually written) https://github.com/cardillo/joinery/issues/74
+    @Test
+    public void test2ColNum(){
+        DataFrame<Object> df = new DataFrame<>("name", "price", "onSale");
+        df.append(Arrays.asList("bag1", 30, true));
+        df.append(Arrays.asList("bag2", 25, false));
+        df.append(Arrays.asList("bag3", 20, false));
+        df.append(Arrays.asList("bag4", 15, true));
+        System.out.println(df.columns());
+        assertEquals(-1, df.numOfCol("pri"));
+        assertEquals(-1, df.numOfCol("on_Sale"));
+        //        System.out.println(df.row(1));
+    }
+}

src/test/java/joinery/impl/SerializationTest.java

@@ -0,0 +1,44 @@
+//package joinery.impl;
+//
+//import joinery.DataFrame;
+//import junit.framework.TestCase;
+//import org.junit.Test;
+//
+//import javax.xml.crypto.Data;
+//import java.sql.Connection;
+//import java.sql.Date;
+//import java.sql.DriverManager;
+//import java.sql.SQLException;
+//
+//public class SerializationTest extends TestCase {
+//
+//    // issue #92, Use readsql() to read data from the database, the types obtained are not all strings, can be numbers, dates, etc.
+//    public void testReadSql() throws SQLException {
+//        Connection c = DriverManager.getConnection("jdbc:derby:memory:testdb;create=true");
+//        c.createStatement().executeUpdate("create table data2 (a varchar (20), b double )");
+//        c.createStatement().executeUpdate("insert into data2 values ('2022-04-24', 20.02)");
+//        c.createStatement().executeUpdate("insert into data2 values ('2022-04-25', 40.44)");
+////        List<Object> other = DataFrame.readSql(c, "select * from data").flatten();
+//        DataFrame<Object> other = DataFrame.readSql(c, "select * from data2");
+//        assertTrue(other.get(0, 0) instanceof Date);
+//        assertTrue(other.get(1, 0) instanceof Date);
+//        assertTrue(other.get(0, 1) instanceof Double);
+//        assertTrue(other.get(1, 1) instanceof Double);
+//    }
+//
+//    // issue #92, Use readsql() to read data from the database, the types obtained are not all strings, can be numbers, dates, etc.
+//    public void testReadSql2() throws SQLException {
+//        Connection c = DriverManager.getConnection("jdbc:derby:memory:testdb;create=true");
+//        c.createStatement().executeUpdate("create table data (a varchar (20), b varchar(10) )");
+//        c.createStatement().executeUpdate("insert into data values ('04-24', '20')");
+//        c.createStatement().executeUpdate("insert into data values ('04-25', '40')");
+//        c.createStatement().executeUpdate("insert into data values ('4-40', '60')");
+////        List<Object> other = DataFrame.readSql(c, "select * from data").flatten();
+//        DataFrame<Object> other = DataFrame.readSql(c, "select * from data");
+//        assertTrue(other.get(0, 0) instanceof Date);
+//        assertTrue(other.get(1, 0) instanceof Date);
+//        assertTrue(other.get(2, 0) instanceof Date);
+//        assertTrue(other.get(0, 1) instanceof Integer);
+//        assertTrue(other.get(1, 1) instanceof Integer);
+//    }
+//}