Hi, The following shows that do.call of `c` on a list of IRangesList returns "list" only when the list is named. > library(IRanges) >example(IRangesList) > class(x) [1] "CompressedIRangesList" attr(,"package") [1] "IRanges" > class(do.call(c,list(x1=x,x2=x))) [1] "list" I am confused this. I would not expect the fact that the list is named to have any impact on the result. But, look, omitting the list names the class is now an IRangesList > class(do.call(c,list(x,x))) [1] "CompressedIRangesList" attr(,"package") [1] "IRanges" > class(c(x,x)) [1] "CompressedIRangesList" attr(,"package") [1] "IRanges" A 'workaround' is to unname the list, as demonstrated: > class(do.call(c,unname(list(x1=x,x2=x)))) [1] "CompressedIRangesList" attr(,"package") [1] "IRanges" But, why does having a 'names' attribute effect the behavior of do.calling `c` so much as to change the class returned? Thanks for your help/education..... Malcolm Cook Computational Biology - Stowers Institute for Medical Research > sessionInfo() R version 2.15.1 (2012-06-22) Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit) locale: [1] C attached base packages: [1] stats graphics grDevices utils datasets methods base other attached packages: [1] IRanges_1.16.4 BiocGenerics_0.4.0 loaded via a namespace (and not attached): [1] AnnotationDbi_1.20.3 BSgenome_1.26.1 Biobase_2.18.0 Biostrings_2.26.2 DBI_0.2-5 GenomicFeatures_1.10.1 GenomicRanges_1.10.5 RCurl_1.95-3 RSQLite_0.11.2 Rsamtools_1.10.2 XML_3.95-0.1 biomaRt_2.14.0 bitops_1.0-4.2 colorspace_1.2-0 data.table_1.8.6 functional_0.1 graph_1.36.1 gtools_2.7.0 parallel_2.15.1 rtracklayer_1.18.1 stats4_2.15.1 tools_2.15.1 zlibbioc_1.4.0 >