As Altenbach noted in the response cited by Uday, when you plot a graph, you are sending the entire array to the Plot, so clearing the graph is simply the action of writing an empty array to it.
On the other hand, when you use the Express XY Graph, you are creating an ever-expanding Array, as each point that you add gets appended to an Array kept internally in the Express VI. Generally, appending to the end of an Array is, perhaps, the slowest and most memory-intensive way to "grow" an array. Of course, this sub-optimal behavior is "hidden" inside the Express VI.
Is this really something that you want to do? Do you want to see each point on the Graph be added, one at a time? Are you really plotting a graph, where X and Y are independent variables (as opposed to a chart, where there is no explicit X, as it is an implicit implementing variable, such as Time)? [Wow, that's an awkward sentence ...].
Having said all that, I have used "Graphs as Charts", but I had a specific problem in mind, and managed the memory myself (I don't quite remember the details, but suspect Queues might have been involved ...).
If you really do want a Chart, I'd say "Replace the Graph by a Chart". Note that clearing a Chart involves writing an empty array into its "storage" location, called its "History", which you do using a Property Node.
Bob Schor
