[R] Why does "summary" show number of NAs as non-integer?

[Earl F. Glynn]

Example:

> set.seed(19)
> summary( c(NA, runif(10,1,100), NaN) )
   Min. 1st Qu.  Median    Mean 3rd Qu.    Max.    NA's
  7.771  24.850  43.040  43.940  63.540  83.830   2.000

Why isn't the number of NA's just "2" instead of the "2.000" shown above?

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