Command Reference : Working with Graphs : Changing Graph Types
  
Changing Graph Types
You may change the graph type of a named graph object by following the object name with the desired graph type keyword and any options for that type. For example:
grsales.bar(l)
converts the bar graph GRSALES, created above, into a mixed bar-line graph, where SALES1 is plotted as a bar graph and SALES2 is plotted as a line graph within a single graph.
Note that specialized graphs, such as boxplots, place limitations on your ability to change the graph type. In general, your ability to customize the graph settings is more limited when changing graph types than when generating the graph from the original data.
Graph options are generally preserved when changing graph types. This includes attributes such as line color and axis assignment, as well as objects added to the graph, such as text labels, lines and shading. Commands to modify the appearance of named graph objects are described in “Customizing a Graph”.
Note, however, that the line and fill graph settings are set independently. Line attributes apply to line and spike graphs, while fill attributes apply to bar, area, and pie graphs. For example, if you have modified the color of a line in a spike graph, this color will not be used for the fill area if the graph is changed to an area graph.