Returns the most frequent element of `data,' which should be a sequence. The algorithm involves sorting, and so the data must be numbers or the `key' function must produce numbers. Consider `sxhash' if no better function is available. Also returns the number of occurrences of the mode. If there is more than one mode, this returns the first mode, as determined by the sorting of the numbers. Keep in mind that if the data has multiple runs of like values that are bigger than the window size (currently defaults to 10% of the size of the data) this function will blindly pick the first one. If this is the case you probabaly should be calling `mode' instead of this function.