Hello

I tried to reproduce the analysis in GenomicFeatures vignette section 2.7.2 (Example: Retrieving data from an RNA-seq experiment); 
I got the error below. Can you please help me?
Thanks


> txdb <- loadFeatures(system.file("extdata", "UCSC_knownGene_sample.sqlite", package="GenomicFeatures"))
> gr <- GRanges(seqnames = rep("chr5",4), ranges = IRanges(start = c(244620,244670,245804,247502), end = c(244652,244702,245836,247534)), strand = rep("+",4)) 
> annotGR <- transcriptsByRanges(txdb, gr, columns=c("tx_id", "tx_name", "gene_id", "exon_id")) 
> OL <- findOverlaps(gr, annotGR, multiple=TRUE) 
> tdata <- annotGR[subjectHits(OL),] 

> table(tdata$tx_id) 
Error in x[[name, exact = FALSE]] : 
  missing '[[' method for Sequence class GRanges
> table(unlist(tdata$gene_id))
Error in x[[name, exact = FALSE]] : 
  missing '[[' method for Sequence class GRanges
Error in unlist(tdata$gene_id) : 
  error in evaluating the argument 'x' in selecting a method for function 'unlist'
> 

> sessionInfo()
R version 2.11.0 Under development (unstable) (2010-02-21 r51163) 
x86_64-unknown-linux-gnu 

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=C              LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C            
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] GenomicFeatures.Mmusculus.UCSC.mm9_0.1.1
 [2] GenomicFeatures_0.3.38                  
 [3] ShortRead_1.5.18                        
 [4] lattice_0.18-3                          
 [5] BSgenome_1.15.10                        
 [6] Biostrings_2.15.22                      
 [7] IRanges_1.5.49                          
 [8] rtracklayer_1.7.10                      
 [9] RCurl_1.3-1                             
[10] bitops_1.0-4.1                          

loaded via a namespace (and not attached):
[1] Biobase_2.7.4 biomaRt_2.3.4 DBI_0.2-5     grid_2.11.0   hwriter_1.1  
[6] RSQLite_0.8-3 tools_2.11.0  XML_2.6-0    
> 


      
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