Elegant way to report missing values in a data.frame

Just use sapply

> sapply(airquality, function(x) sum(is.na(x)))
  Ozone Solar.R    Wind    Temp   Month     Day 
     37       7       0       0       0       0

You could also use apply or colSums on the matrix created by is.na()

> apply(is.na(airquality),2,sum)
  Ozone Solar.R    Wind    Temp   Month     Day 
     37       7       0       0       0       0
> colSums(is.na(airquality))
  Ozone Solar.R    Wind    Temp   Month     Day 
     37       7       0       0       0       0