[Rd] fivenum accuracy (PR#13164)

[dleong at analogic.com]

Full_Name: David Leong
Version: 2.7.2
OS: Windows XP
Submission from: (NULL) (12.187.86.2)


It appears for the fivenum function, there is a strait average between two
ranked samples. This should be a linear interpolation between ranks.
For the following data set

#data
CaCO3<-c(130.8,129.9,131.5,131.2,129.5,132.7,131.5,127.8,133.7,132.2,134.8,131.7,133.9,129.8,131.4,128.8,132.7,132.8,131.4,131.3)

fivenum reports 127.80 130.35 131.45 132.70 134.80

130.35 should be 130.125. The other are correct.

For the 20 points, the rank is (20+1)/4=5.25 so the weighting factor is 0.25 not
0.5.