A DataFrame is a two-dimensional data container, similar to a Matrix, but which can contain heterogeneous data, and for which symbolic names may be associated with the rows and columns.

Each column of a DataFrame is a DataSeries, and the column labels may be used to refer to the corresponding column.

df := DataFrame( < 1, 2, 3; 4, 5, 6 >, 'rows' = [ 'a', 'b' ], 'columns' = [ 'A', 'B', 'C' ] );

$\mathrm{df}≔\left[\begin{array}{cccc}& A& B& C\\ a& 1& 2& 3\\ b& 4& 5& 6\end{array}\right]$

type( df[ 'B' ], DataSeries );

$\mathrm{true}$

Since each column is a DataSeries, you can index hierarchically into the columns of a DataFrame to extract individual data elements.

df[ 'B' ][ 1 ];

$2$

df[ 'B' ][ 'b' ];

$5$

However, you can also select individual data items by specifying the desired row and column indices directly.  (Row and column indices may be either numeric, by position, or symbolic.)

df[ 1, 2 ];

$2$

df[ 'a', 'B' ];

$2$

You can use a range or list to select specified columns. In the case of a list, they can come in any desired order.

df[ 'A' .. 'B'];

$\left[\begin{array}{ccc}& A& B\\ a& 1& 2\\ b& 4& 5\end{array}\right]$

df[ [ 'B', 'C', 'A' ] ];

$\left[\begin{array}{cccc}& B& C& A\\ a& 2& 3& 1\\ b& 5& 6& 4\end{array}\right]$

For more information on indexing a DataFrame, see DataFrame,indexing.