A wrapper for subset() method with proper set of attributed
mda.subset(x, subset = NULL, select = NULL)dataset (data frame or matrix)
which rows to keep (indices, names or logical values)
which columns to select (indices, names or logical values)
a data with the subset
The method works similar to the standard subset() method, with minor differences. First of all
it keeps (and correct, if necessary) all important attributes. If only columns are selected, it keeps
all excluded rows as excluded. If only rows are selected, it keeps all excluded columns. If both rows
and columns are selected it removed all excluded elements first and then makes the subset.
The parameters subset and select may each be a vector with numbers or nanes without excluded
elements, or a logical expression.