I solved it. It was quite easy: Because each test is a list, it's necessary to specify which element contains the comparison matrix (p values). Let me show it:
>show(test) An object of class “pairwise.htest” $method [1] "Wilcoxon rank sum test" $data.name [1] "SAND and Organ" $p.value FlowerA FlowerB FlowerC FlowerD LeafA FlowerB 0.000617030 NA NA NA NA FlowerC 0.000617030 0.004319210 NA NA NA FlowerD 0.000617030 0.000617030 0.000617030 NA NA LeafA 0.006141902 0.006141902 0.006141902 0.006141902 NA LeafC 0.000617030 0.000617030 0.000617030 0.000617030 0.3242459 $p.adjust.method [1] "bonferroni" >multcompLetters(test$p.value) FlowerB FlowerC FlowerD LeafA LeafC "a" "b" "c" "d" "e" Thank you! Retama -- View this message in context: http://www.nabble.com/Letter-based-representation-of-pairwise-comparisons-tp21350364p21787201.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.