Re. the Omit question:
I find the expression "extract out" a bit confusing. Does it mean:
I wish to extract only the rows with NA ... ? (That is to include them in the result).
or does it mean
I wish to omit the rows with NA ...? (That is, to exclude them from the result).
I shall have to take pot luck! (I did and I was right!)
You never know: reading my book: "All about your computer" might just tell you something you never knew!