string strCMD;
int nSkipPoints = 4;  // skip points is 4
strCMD.Format("set %s -skip %d;", dp.GetDatasetName(), nSkipPoints);  // dp is the data plot object
gl.LT_execute(strCMD);  // execute the LabTalk command, gl is the graph layer of the data plot

// Arguments:
// const string strNewData: the name of the new data
// int nPlotIndex = -1: the index of the plot in the layer to be changed data
void test_changeplotdata(const string strNewData, int nPlotIndex = -1)
{
	GraphLayer glActive = Project.ActiveLayer();  // get the active graph layer
	if(!glActive)
	{
		out_str("Error, please the active window is graph.");
		return;
	}

	DataPlot dp = glActive.DataPlots(nPlotIndex);  // get the data plot by index
	if(!dp)
	{
		out_str("Error, not found data plot by index.");
		return;
	}
	if( nPlotIndex < 0 ) // -1 means active plot index, need to convert to real index
		nPlotIndex = dp.GetIndex();

	Tree trContents;
	glActive.GetLayerContents( trContents, GETLC_DATAPLOTS );	// get layer contents tree
	TreeNode trLayer = trContents.GetNode( "Layer" + glActive.GetIndex() ); // layer tree node, the index offset is 0 here
	if( !trLayer )
	{
		out_str("Error");
		return;
	}
		
	string strName = "DataPlot" + (string)( nPlotIndex + 1 ); // the index offset is 1 here
	TreeNode trDataPlot = trLayer.GetNode(strName);	  // data plot tree node
	if( trDataPlot )
	{
		TreeNode trDepData = trDataPlot.PlotDesigs.DPC1;
		if( trDepData && trDepData.Name )
		{   	
			trDepData.Name.strVal = strNewData;  // replace with the new data name
			DWORD dwAddPlotsCtrl = ADDPLOTSFROMTREE_EDIT|ADDPLOTSFROMTREE_IMPLICIT_STYLEHOLDERS;
			int nNewPlotNum = glActive.AddPlots( trContents.FirstNode, dwAddPlotsCtrl );
		}
	}
}