1. A method for providing an output histogram corresponding to a plurality of data signals without revealing individual data signals forming the plurality, the method comprising: receiving a plurality of array sketches, each array sketch being determined from a different one of the plurality of data signals; adding the plurality of array sketches to yield an array sketch of the vector sum of the array sketches; constructing a robust histogram from the array sketch of the vector sum, constructing the output histogram from the array sketch and the robust histogram via a hybrid histogram; wherein the output histogram is used for observing a traffic pattern in a network without revealing individual data signals.