Question: A question when using Biostrings
gravatar for Hervé Pagès
4.1 years ago by
Hervé Pagès ♦♦ 13k
United States
Hervé Pagès ♦♦ 13k wrote:
Hi Xiaoyun, On 10/21/2013 06:50 AM, Xiaoyun Shang wrote: > Dear Pages, > > Biostrings is a great package in R. Thank you all! > > I had a question when I used this package to deal with a fasta file. > Here is my code: > > library("Biostrings") > human_protein <- readAAStringSet("HUMAN.fasta","fasta",use.names=TRUE) > names(human_peotein[[1]]) > > When I use the function 'names' to extract the name of first name, it > returns 'NULL', but it do have a name (description). How can I get this > name included in the fasta file? You need to understand the subtle but fundamental difference between [[ and [ on a list-like object: x <- list(A=1:3, B=c(x=1, y=2), C=NULL, D=2:-1) 'x' is a named list: > names(x) [1] "A" "B" "C" "D" Those names are the "outter names" (aka "top-level names") of the list. The 1st list element is an integer vector of length 3: > x[[1]] [1] 1 2 3 > length(x[[1]]) [1] 3 It has no names: > names(x[[1]]) NULL The 2nd list element is an integer vector of length 2: > x[[2]] x y 1 2 It has names: > names(x[[2]]) [1] "x" "y" Those names are the "inner names" of the 2nd list element. To extract the 1st *outter* name of the list, do: > names(x)[1] [1] "A" You could get the same result with (note the use of the single bracket here): > names(x[1]) [1] "A" This works because: x[1] is still a list like 'x' but only the 1st element of the list was kept (so it's a list of length 1). And also because [ subsets the *outter* list names: > length(x[1]) [1] 1 > x[1] $A [1] 1 2 3 Note that, even if semantically equivalent, 'names(x)[i]' is preferred over 'names(x[i])'. The 'human_protein' object you got with readAAStringSet() is an AAStringSet object, which is a list-like object. So the same apply. Hope this helps, H. > > Many thanks! > > Xiaoyun > > -- > Xiaoyun Shang MD, PhD > Institute of Immunology, PLA > Third Military Medical University > 30# Gaotanyan, Shapingba,Chongqing > 400038 P.R.China > phone: +86 23 6877 1920 <tel:%2b86%2023%206877%201920> > mobile?+86-135 2748 0908 <tel:%2b86-135%202748%200908> > Email: shangxiaoyun at <mailto:shangxiaoyun at=""""> ; > shangxiaoyun at <mailto:shangxiaoyun at=""""> -- Hervé Pagès Program in Computational Biology Division of Public Health Sciences Fred Hutchinson Cancer Research Center 1100 Fairview Ave. N, M1-B514 P.O. Box 19024 Seattle, WA 98109-1024 E-mail: hpages at Phone: (206) 667-5791 Fax: (206) 667-1319
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