# #################################################
# Function for generating a frequency list of words or other (linguistic)
# features. It basically counts the elements of a vector and returns a vector
# of these elements in descending order of frequency.
# Refer to help(make.frequency.list) for farther details.
# #################################################

make.frequency.list = function(data, 
                               value = FALSE,
                               head = NULL,
                               relative = TRUE) {
     
                                       
                                       
     #####################################
     # first, sanitize the input dataset
     
     # test if the dataset belongs to 'stylo.corpus' class
     if(class(data) == "stylo.corpus" | is.list(data) == TRUE) {
             # unlist, or make one long text out of the corpus samples
             data = unlist(data, recursive = FALSE, use.names = FALSE)    
     # otherwise, test if the dataset is a vector
     } else if(is.vector(data) == FALSE) {        
             # whet it is not, produce an error message and stop
             stop("unable to make a list of frequencies")
     }
     
     # test if the dataset has at least two elements
     if(length(data) < 3) {
             stop("you try to measure frequencies of an empty vector!")
     }
     #####################################


     
     #####################################     
     # the dataset sanitized, let counting the features begin!     
     frequent.features = sort(table(data), decreasing = TRUE)
     #####################################

     
     # if relative frequencies were requested, they are normalized
     if(relative == TRUE) {
             frequent.features = frequent.features / length(data) * 100
     }
     
     # additionally, one might limit the number of the most frequent features;
     # this will return first n elements only (this is the argument 'head')
     if(is.numeric(head) == TRUE) {
             # sanitizing the indicated number
             head = abs(round(head))
             if(head == 0) {head = 1}
             # cutting off the list
             frequent.features = frequent.features[1:head]
     }
     
     # in most cases, one needs just a list of features, without frequencies
     if(value == FALSE) {
             frequent.features = names(frequent.features)
     }
     
     
return(frequent.features)     
}