[R] summary() vs mean()
Marc R. Feldesman
feldesmanm at pdx.edu
Thu Feb 1 04:14:42 CET 2001
Forgive what may seem to be a trivial question/problem.
Below is some simple R 1.2.1(Windows) code with output.
> summary(mammals, digits=10)
Name Body.Weight Brain.Weight
Red Fox :1 Min. : 3.0 Min. : 26.0
Pig :1 1st Qu.: 35.5 1st Qu.: 138.5
Man :1 Median : 100.0 Median : 406.0
Kangaroo:1 Mean : 761.2 Mean :1000.0
Jaguar :1 3rd Qu.: 493.0 3rd Qu.: 667.5
Horse :1 Max. :6654.0 Max. :5712.0
(Other) :9
> mean(mammals[,3])
[1] 1000.467 # <---summary() reports it as 1000.0
> mean(mammals[,2])
[1] 761.2 # <- summary() reports it as 761.2
I'm puzzled why the Brain.Weight mean from summary() is different from
mean(mammals[,3]), while the Body.Weight means are identical in the two
functions. This isn't limited to R; I've observed the same thing in S-Plus
2000 (and v.6 beta).
I can get the "right" answer in S-Plus using the digits argument (setting
digits=8), but this argument doesn't seem to have any effect in R 1.2.1. I
*did* use it the way it is illustrated in the help file as well (e.g.
summary(mammals, digits=max(10, getOption("digits")))
)
with the same results as above.
So, I guess I have two questions:
1) Why does S (in both S-Plus and R 1.2.1) produce different values for
the means in the second variable but not the first?
2) Why does the digits argument seem not to have any effect in R 1.2.1's
summary()?
P.S. I also pasted the example code from the summary help file into the R
1.2.1 window. The digits argument doesn't change the results there either.
Dr. Marc R. Feldesman
email: feldesmanm at pdx.edu
email: feldesman at attglobal.net
fax: 503-725-3905
"Don't know where I'm going.
Don't like where I've been.
There may be no exit.
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