title: Add a new row to R dataframe - but if does not exist already?
body: <p>Is there any possiblity to add a new row that does not exist already in a dataframe? I create a big dataframe (100k records) with different combinations of the variables (randomly selected) and I want to add them to the existing dataframe with a condition: all they must be different (at least one variable must be different). </p>