I have imported 2 sets of sequences in fasta format and imported them as DNAStringSets using decipher (which I believe uses biostrings for the basic manipulation of nucleic acts string sets):

> extraemm_DNA_untrim1

A DNAStringSet instance of length 5
    width seq                                                 names               
[1]   346 GCATCCGTAGCGGTCGCTGTGGCT...AAGATGTAGAACGTCACTATCTTA EMM88 emm88.0 (em...
[2]   391 GCATCAGTAGCGGTTGCTTTGACT...AATTAGCGGATAAGCAAGAACATC EMM225 emm225.0 (...
[3]   499 GGTACTGCTTCAGTAGCGGTTGGT...AAGAAGCAGAGCAGAAAAAACTTA EMM52 emm52.0 (em...
[4]   360 GCATCCGTAGCAGTCGCTGTGGCT...GAACGCCAAAGTCAACGAGAAGTC EMM2 emm2.0 (emm-...
[5]   384 AGCAGTTGCTGTGGCTGTTTTAGG...AATAGACAAGCGTTATCAAGAACA EMM114 emm114.0 (...
> extraemm_DNA_untrim2

A DNAStringSet instance of length 5
    width seq                                                 names               
[1]   345 CATCCGTAGCGGTCGCTGTGGCTG...AAGATGTAGAACGTCACTATCTTA EMM88 emm88.0 (em...
[2]   390 CATCAGTAGCGGTTGCTTTGACTG...AATTAGCGGATAAGCAAGAACATC EMM225 emm225.0 (...
[3]   498 GTACTGCTTCAGTAGCGGTTGGTT...AAGAAGCAGAGCAGAAAAAACTTA EMM52 emm52.0 (em...
[4]   359 CATCCGTAGCAGTCGCTGTGGCTG...GAACGCCAAAGTCAACGAGAAGTC EMM2 emm2.0 (emm-...
[5]   383 GCAGTTGCTGTGGCTGTTTTAGGA...AATAGACAAGCGTTATCAAGAACA EMM114 emm114.0 (...
 

Very simply I would like to get a new DNAStringSet with sequences 1 and 2 from extraemm_DNA_untrim1  and 3, 4 and 5 from extraemm_DNA_untrim2.

I realise this is probably a very simple question, but I can not find much simple documentation on Biostrings basics and I am quite new to using it.

Thanks

You can select entries in a DNAStringSet using the [] notation, and you can combine DNAStringSets using c(). So if you want to select the first two entries from one, entries 3 to 5 from the other and then combine you can do:

c( extraemm_DNA_untrim1[1:2], extraemm_DNA_untrim2[3:5] )

Here's a little toy example:

> ## create two BStringSets
> bs1 <- BStringSet(c("A1", "A2", "A3", "A4"))
> bs2 <- BStringSet(c("B1", "B2", "B3", "B4"))
> 
> ## Print them out so we can see the contents
> bs1
  A BStringSet instance of length 4
    width seq
[1]     2 A1
[2]     2 A2
[3]     2 A3
[4]     2 A4
> bs2
  A BStringSet instance of length 4
    width seq
[1]     2 B1
[2]     2 B2
[3]     2 B3
[4]     2 B4
> 
> ## combine first two entries from one, last two from the other
> c(bs1[1:2], bs2[3:4])
  A BStringSet instance of length 4
    width seq
[1]     2 A1
[2]     2 A2
[3]     2 B3
[4]     2 B4