[R] Replacing multiple elements in a vector !

[Steve Lianoglou]

Hi,

On Oct 22, 2009, at 10:12 AM, Praveen Surendran wrote:

> Hi,
>
> I have a vector with elements
>
> rs.id=c('rs100','rs101','rs102','rs103')
>
> And a dataframe 'snp.id'
>
> 1              SNP_100              rs100
> 2              SNP_101              rs101
> 3              SNP_102              rs102
> 4              SNP_103              rs103
>
> Task is to replace rs.id vector with corresponding 'SNP_' ids  in  
> snp.id.


First, please post your code and data in such a way that it's easy for  
those of us trying to help you to paste into our R session quickly,  
for instance, a better way to have given your data.frame would have  
been like so:

R> > rs.id=c('rs100','rs101','rs102','rs103')
R > df <- data.frame(snp.id=paste("SNP", 100:103, sep="_"),  
rs.id=rs.id, )

Now, assuming rs.id <-> snp.id is a one-to-one mapping:

1. One way to get the appropriate df$snp.id for each value in your  
rs.id vector is to use ``match``:

R> df$snp.id[match(rs.id, df$rs.id)]
[1] "SNP_100" "SNP_101" "SNP_102" "SNP_103"

2. Alternatively, you can use the "rs*" values as the rownames of your  
data.frame, and use the rs.id value to select:

R> rownames(df) <- df$rs.id
R> df[rs.id, 'snp.id']
[1] "SNP_100" "SNP_101" "SNP_102" "SNP_103"


-steve

--
Steve Lianoglou
Graduate Student: Computational Systems Biology
   |  Memorial Sloan-Kettering Cancer Center
   |  Weill Medical College of Cornell University
Contact Info: http://cbio.mskcc.org/~lianos/contact