I'm working now with some really big dataframes and in order to shorten the calculations I need to exclude rows with NA values, but after the calculation and creating new dataframe I need to bring them back (to the new dataframe). Is there any possibility to track which rows I exclude? 

for example:

```
   X1 X2 X3 X4
1  3  4  5  4
2  3  3  3  4
3  NA NA NA NA
4  4  3  3  2

```

So what I want is to get after "complete.cases" number 3, that refers to the row number with NA that was excluded. Is it possible without adding extra column with numbering?