[BioC] unlist changes the length?

[Irene Li]

Hi bioconductor users,

I am learning bioconductor by following the on-line short courses. This was 
what happened when I tried some code in "Differential expression"
>library(annotate)
>library(hgu95av2)
>chr <- getCHR(geneNames(ALLSub), "hgu95av2")
Error: couldn't find function "getCHR"
>chr <- mget(geneNames(ALLSub), env=hgu95av2CHR)
>ll <- getLL(geneNames(ALLSub), "hgu95av2")
>ll.chr <- tapply(chr, ll, unique)
Error in unique.default(X[[as.integer(1)]], ...) :
        unique() applies only to vectors
>ll.chr <- tapply(unlist(chr), ll, unique)
Error in tapply(unlist(chr), ll, unique) :
        arguments must have same length
>length(chr)
[1] 2400
>length(ll)
[1] 2400
>length(unlist(chr))
[1] 2408
>

Is this caused by a bug in "unlist" like an unaccessable link in google 
search said, or I have done something wrong here? how can I solve this 
problem?

Thanks.

Irene