This function will sextract a part of a list based on the length of its components. Typically
a genebag list can be used. This function will work for uniclass lists of vectors and data frames.
: default = 0 and this has no action. This is the lower threshold for the element's size.
max.size
: default = 0 and this has no action. This is the upper threshold for the element's size.
names
: default = FALSE the function will return a subset of the list, if TRUE the function will
return only the names of the elements of the list as identifiers.