Data as a "matrix", a "data.frame" or even a "vector" or "factor". "vector" or "factor" are coerced to a "data.frame" with one column.
catgories
optional a vector ("numeric" or "character") containig the categories to tabulate. At default (catgories=NULL) the fuction looks for unique categories in X.
na.omit
logical (default: na.omit=FALSE ) wether to return frequencies for missing values, NAs.
Details
X can either be a ("numeric" or "character") "matrix" containing response vectors of persons (rows) or a "data.frame" containing "numeric", "character" or "factor" variables (columns).