// ShuffleN randomly shuffles the first n item in the data slice. It uses
// Knuth's shuffle algorithm. Panics if n is larger than data.Len()-1 or is
// negative.
func ShuffleN(data goutil.SwapInterface, n int) {
if n < 0 {
panic("ShuffleN with negative n")
}
if n > data.Len() {
panic("ShuffleN n too large")
}
for i := 0; i < n; i++ {
data.Swap(i, Rand(i, n))
}
}
// Shuffle randomly shuffles the all the item in the data slice.
func Shuffle(data goutil.SwapInterface) {
ShuffleN(data, data.Len())
}