Convert one DataFrame to other or copy dataframes

Signed-off-by: Aravinda VK <vkaravinda7@gmail.com>

Author: aravindavk

README.md

@@ -207,3 +207,21 @@ foreach (record;file.byLine.joiner("\n").csvReader!ItemCsvData(header: null))
 // Preview the imported data
 df.writeln;
 ```
+
+## Copying the DataFrame or creating DataFrame of new Type
+
+To create a `PriceList` dataframe from the list of items.
+
+```d
+struct PriceList
+{
+    string name;
+    double price;
+}
+
+df.rows
+    .sort!("a.name < b.name")
+    .uniq!("a.name == b.name")
+    .to_df!PriceList
+    .writeln;
+```

source/dataframes/package.d

@@ -199,6 +199,20 @@ class DataFrame(T)
 
         return output.data;
     }
+
+    DataFrame!T to_df()
+    {
+        return to_df!T;
+    }
+
+    DataFrame!T1 to_df(T1)()
+    {
+        auto output = new DataFrame!T1;
+        foreach(r; this.rows)
+            output.add(r.toDataFrameStruct!T1);
+
+        return output;
+    }
 }
 
 unittest
@@ -285,4 +299,27 @@ unittest
     assert(result[3].name == "C");
     assert(result[4].name == "D");
     assert(result[5].name == "E");
+
+    struct PriceList
+    {
+        string name;
+        double price;
+    }
+
+    auto items = df.rows
+        .sort!("a.name < b.name")
+        .uniq!("a.name == b.name")
+        .to_df!PriceList;
+
+    assert(items.length == 5);
+    assert(items.ncol == 2);
+    assert(items.columnNames == ["name", "price"]);
+
+    auto dfCopy = df.to_df;
+    assert(dfCopy.ncol == 4);
+    assert(dfCopy.nrow == 6);
+
+    auto itemsDf = df.to_df!PriceList;
+    assert(itemsDf.ncol == 2);
+    assert(itemsDf.nrow == 6);
 }

source/dataframes/rows.d

@@ -44,4 +44,28 @@ struct Row(T)
 
         return output.data ~ ")";
     }
+
+    T1 toDataFrameStruct(T1)()
+    {
+        alias outputFieldNames = FieldNameTuple!(T1);
+        T1 output;
+
+        static foreach(name; outputFieldNames)
+        {
+            static if(hasMember!(T, name))
+                __traits(getMember, output, name) = __traits(getMember, this, name);
+        }
+
+        return output;
+    }
+}
+
+DataFrame!T to_df(T, Range)(Range rows)
+{
+    auto df = new DataFrame!T;
+
+    foreach(row; rows)
+        df.add(row.toDataFrameStruct!T);
+
+    return df;
 }