There are faster ways of accomplishing your task in Matlab.
First, let's examine if there is a function that will do what you want. Type 'methods double' for a list of functions that can act on the data type 'double'. This is not an exhaustive list, but it gives a good starting point. For example, the function 'accumarray' looks promising. However, brief experimentation does not give better results. After running through the remainder of the list, it does not look likely that a single builtin function will do what you want.
You also question if there is an already known approach that is faster. There is such an approach, and it is well known. MEX functions are functions written in C or Fortran that are compiled to be called from Matlab. Type 'doc mex' for more information. Often, this improves the final runtime of a function. With care in the implementation, this approach will improve the runtime for your case as well.
