Selecting columns from an laf object works as it does for a
data.frame.
# S4 method for laf
[[(x, i)# S4 method for laf
$(x, name)
an object of type laf
index of column to select. This should be a numeric or character vector.
the name of the column to select.
Returns an object of type laf_column. This object behaves almost the
same as an laf object except that is it no longer necessary
(or possible) to specify which column should be used for functions that
require this.