I don't think there is a LabTalk solution to this but you can use the following Origin C code and call it from labTalk.
void del_alternate_rows(BOOL nUndo = 1)
{
Worksheet wks = Project.ActiveLayer();
int nRows = wks.GetNumRows();
// generate array of row index to delete
// alternate rows, so (0-offset) 1,3,5,7,..
if(nRows > 0)
{
vector<int> nvAlternateRows;
nvAlternateRows.Data(1, nRows-1, 2);
wks.SetSelectedRange( nvAlternateRows );
wks.DeleteSelection( nUndo );
}
else
printf("empty worksheete, not enough rows to delete");
}
CP