How it works...

The na.omit() function internally uses the is.na() function, that allows us to find whether its argument is NA. When applied to a single value, it returns a Boolean value. When applied to a collection, it returns a vector:

> is.na(dat[4,2]) 
[1] TRUE 
 
> is.na(dat$Income) 
[1] FALSE FALSE FALSE FALSE FALSE  TRUE FALSE FALSE FALSE 
[10] FALSE FALSE FALSE  TRUE FALSE FALSE FALSE FALSE FALSE 
[19] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE