Q:

Length of longest stretch of NAs in a column of data-frame object

I want to write a code that finds the length of longest continuous stretch of NA values in a column of a data-frame object.
>> df   
      [,1] [,2] 
[1,]    1    1   
[2,]   NA    1   
[3,]    2    4   
[4,]   NA    NA   
[6,]    1    NA   
[7,]   NA    8
[8,]   NA    NA
[9,]   NA    6
# e.g.
>> longestNAstrech(df[,1])
>> 3
>> longestNAstrech(df[,2])
>> 2
# What should be the length of longestNAstrech()?

A:

Using base R we could create a function 
longestNAstrech <- function(x) {
  with(rle(is.na(x)), max(lengths[values]))  
}

longestNAstrech(df[, 1])
#[1] 3

longestNAstrech(df[, 2])
#[1] 2

