Preheat the oven to 450 degrees F. Grease a 1/2 sheet pan. In a mixing bowl, combine the flour, baking powder, baking soda, salt, and sugar together. Add the butter, and with your hands, work the butter into the flour mixture until the mixture resembles a coarse cornmeal. Stir in the sweet potatoes and pecans. Add the cream, a little at a time until a soft dough is formed. Lightly flour a surface. Place the dough onto the surface and dust the top with flour. Lightly press the dough out to 1/2 inch thickness. Using a 2 inch biscuit cutter, cut the biscuits into rounds. Place the biscuits on a greased baking sheet and bake for about 15 minutes or until the biscuits are golden brown.