How can I have a triangle heatmap (upper or lower) with heatmap.2 without disturbing the clustering?
Something like a corrplot?
Yes. But corrplot's problem is, the data must range from -1 to 1. In addition, I need dendrogram in my heatmap.
Have you searched the WWW? By only having a triangular heatmap, you would be excluding many data-points from which the very cluster dendrograms that you want to include would have been produced. You may need to be more specific. Have you seen some plot in a publication?
I can think how I would go about doing this via the pairs() functionality, but it's not a rudimentary task.