[Rd] bug in apply with median
Peter Dalgaard BSA
p.dalgaard@biostat.ku.dk
23 Sep 2000 16:55:58 +0200
Larry Ammann <ammann@metronet.com> writes:
> I have found a problem in R version 1.1.1 when using apply with the
> median function.
> The problem can be illustrated with the following data matrix:
>
> X1 X2 X3
> 1 2 3
> 4 5 6
> 7 8 NA
>
> Enter this data matrix as X and then try
> apply(X,2,median,na.rm=T)
> The problem here is that the median function returns a named scalar if
> the number of
> observations is odd, but returns an unnamed scalar if the number of
> observations is
> even. This confuses the apply function in this case at:
for ( i in 1:1000 ) cat("Data frames are not matrices!\n")
> X<-matrix(c(1:8,NA),3,3)
> X
[,1] [,2] [,3]
[1,] 1 4 7
[2,] 2 5 8
[3,] 3 6 NA
> apply(X,2,median,na.rm=T)
[1] 2.0 5.0 7.5
Works fine.
However,
> Z<-data.frame(X)
> apply(Z,2,median,na.rm=T)
Error in names(x) == ans.names : comparison (1) is possible only for vector types
Question is whether this is a bug. Apply() never promised to work on
non-arrays. When applied columnwise, it would anyway be more obvious
to use
> sapply(Z,median,na.rm=T)
X1 X2 X3
2.0 5.0 7.5
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907
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