How to sort and subset data in r

I am trying to sort a row based on the first letters of the cells and i am having hard time to write a code in r.

The above is the example dataset to show how my dataset looks like and i want to subset the whole table based on snp row where the snp column starts with "rs" and "SNP"

Expected table:

Any help is appreciated!!

>Solution :

Alternatively,

df<- read.table(
  text= "
snp allele1 allele2
mmsoop  A   A
rs3122  C   G
SNP1234 T   C
rs3144  A   A",
  header=T
)

df[grep("^(SNP|rs)",df$snp),]

     snp allele1 allele2
2  rs3122       C       G
3 SNP1234       T       C
4  rs3144       A       A