Convert a list of vectors or scalars to a
data.frame with only one row. Names of the columns correspond to
the names of elements in the list. If a vector is one list element it is spread over multiple
columns and named sequentially, e.g.
a = c(5,7) becomes
data.frame(a1 = 5, a2 = 7).
data.frame) with only one row, containing the list elements.