# Spearman's footrule
spearmanDistance <- function(Ra, Rb)
{
  distance <- 0
  for (x in Ra)
  {
    distance <- distance + abs(which(Ra==x)-which(Rb==x))
  }
  return(distance)
}

# Kendall tau distance
kendallDistance <- function(Ra, Rb)
{
  distance <- 0
  for (x in Ra)
  {
    for (y in Rb)
    {
      if (((which(Ra==x)<which(Ra==y)) & (which(Rb==x)>which(Rb==y))) | ((which(Ra==x)>which(Ra==y)) & (which(Rb==x)<which(Rb==y))))
      {
        distance <- distance + 1
      }
    }
  }
  return(distance/2) # x < y
}
# can be normalized by dividing by n(n-1)/2 -> [0,1] with 1 as maximum disagreement
# https://en.wikipedia.org/wiki/Kendall_tau_distance