I have been making contour plots from the same type of data and by the same way for more than 50 times. However, I got this alert "Unable to make graph from this data" when plotting 2 of the data tables. First, so far I can't tell what's different in that two data table. Second, if I switch the order of the two columns in the X, it works.
Does anyone know what possibly could be wrong? Or provide a reference about the restriction of contour plot function.
We have seen this in one other case, and it appears to be a numerical issue with collinear points in the X1-X2 space. Reversing the order changes the numerics of the algorithm used to compute the triangulation. We have this as a open issue and will look at improving the robustness of the algorithm.