Hi

I retrieved an expression set (Illumina HumanHT-12 V3.0) using GEOquery, but I noticed that the expr value where not in log2...

So I tried to do it myself but got an error and since I am no R expert, I don't know much about environment, so I don't know how to solve this. Any idea ? Thanks !

Code :

> eset <- getGEO("GSE35449", GSEMatrix = TRUE)[[1]]
> eset@assayData$exprs <- log2(eset@assayData$exprs)
Error in eset@assayData$exprs <- log2(eset@assayData$exprs) : 
  cannot change value of locked binding for 'exprs'

> sessionInfo()
R version 3.2.4 Revised (2016-03-16 r70336)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)

locale:
[1] LC_COLLATE=French_France.1252  LC_CTYPE=French_France.1252   
[3] LC_MONETARY=French_France.1252 LC_NUMERIC=C                  
[5] LC_TIME=French_France.1252    

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

other attached packages:
 [1] NMF_0.23.3          cluster_2.0.4       rngtools_1.2.4      pkgmaker_0.25.10   
 [5] registry_0.3        limma_3.26.9        GEOquery_2.36.0     Biobase_2.30.0     
 [9] BiocGenerics_0.16.1 ggplot2_2.1.0      

loaded via a namespace (and not attached):
 [1] Rcpp_0.12.4        whisker_0.3-2      magrittr_1.5       splines_3.2.4     
 [5] doParallel_1.0.10  munsell_0.4.3      gridBase_0.4-7     colorspace_1.2-6  
 [9] xtable_1.8-2       foreach_1.4.3      stringr_1.0.0      plyr_1.8.3        
[13] tools_3.2.4        grid_3.2.4         gtable_0.2.0       iterators_1.0.8   
[17] digest_0.6.9       reshape2_1.4.1     RColorBrewer_1.1-2 bitops_1.0-6      
[21] codetools_0.2-14   RCurl_1.95-4.8     dendextend_1.1.8   stringi_1.0-1     
[25] scales_0.4.0       XML_3.98-1.4      

In general you don't want to go digging into the $'s and the @'s of objects, but rather get to them via their accessor functions. Take the time to read through the introductory vignettes in the Biobase package to orient yourself with ExpressionSet objects. In the meantime, you might try something like "exprs(eset) <- log2(exprs(eset))"

But you probably still don't want to do that since you should normalize this data (perhaps rma -- are these affy arrays?) in a more standard/robust manner