On 25/03/2009 7:36 PM, Aldi Kraja wrote:
Hi,
I have a data.frame with many variables for which I am performing the
mean by subgroup, for a pair of variables at a time, where one of them
for each pair defines the subgroup. The subgroups in the x$cm1 are 0, 1
and 2.
x
ph1 cm1
0.2345 2
1.2222 1
2.0033 0
0.0000 2
1.0033 1
0.2345 0
1.2222 2
2.0033 0
0.0000 1
1.0033 2
> meanbygroup <- as.vector(with(x, by(x$ph1, x$cm1, mean)))
You don't need with() here, as you are explicitly extracting the vectors
from x.
> meanbygroup
if the ph1 has no missing values the above statements work fine:
[1] 1.4137000 0.7418333 0.6150000
In the moment that I introduce in the ph1 a missing value in the ph1 as NA
x
ph1 cm1
0.2345 2
NA 1
1.2222 1
.............
the above transforms into
[1] 1.4137000 NA 0.6150000
Question: is there a way I can protect this calculations from the NA
values in the ph1 (some kind of: na.rm=T)?
You could use with(), and extract the vectors from a subset of x:
with(x[!is.na(x$ph1),], by(ph1, cm1, mean))
This is untested. If you had provided sample data in a usable format I
would have tried it, but you didn't, and I'm too lazy to create my own.
Duncan Murdoch
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