lumn names of the data in a list of strings
			
			// Variables used
			var selected_column = selected_item.value;					// Column to be modified, coming from a checkbox or radiobutton
			var column_index = data_columns.indexOf(selected_column);	// Position of the selected column in the data
			var data = [];												// List of the data to be shown
			var data_labels = [];										// List of the data labels to be shown
			var dataset_list = [];										// List of the columns already shown in the chart
		