between <-
function(vec, dframe, sname, colname)
{
# for each vec in column sname of dframe,
# the function returns the corresponding unique
# elements from column colname
mat  = NULL
n = names(dframe)
spk = dframe[,n == sname]
for(j in 1:length(vec)){
temp = spk == vec[j]
o = as.character(unique(dframe[temp,n==colname]))
mat$b = c(mat$b, o)
mat$j = c(mat$j, j)
}
factor(mat$b)
}