使用grepl在R中进行模式匹配

Question

I have a dataframe dat like this

P pedigree cas 1 M rs2745406 T 2 M rs6939431 A 3 M SNP_DPB1_33156641 G 4 M SNP_DPB1_33156664_G P 5 M SNP_DPB1_33156664_A A 6 M SNP_DPB1_33156664_T A

I want to exclude all rows where the pedigree column starts with SNP_ and ends with either G, C, T, or A ( _[GCTA] ). In this case, this would be rows 4,5,6.

How can I achieve this in R? I have tried

multisnp <- which(grepl("^SNP_*_[GCTA]$", dat$pedigree)=="TRUE")

new_dat <- dat[-multisnp,]

My multisnp vector is empty, but I can't figure out how to fix it so that it matches the pattern I want. I think it is my wildcard * usage that is wrong.

Answer 1

You can use the following with .*? (match everything in non greedy way):

multisnp <- which(grepl("^SNP_.*?_[GCTA]$", dat$pedigree))
                              ^^^

Answer 2

You can subset dat like this

new_dat <- dat[!grepl("^SNP_.*_[GCTA]$", dat$pedigree), ]

Regarding the code that you've tried, I'm not sure that grepl("^SNP_*_[GCTA]$") will complete without an error since you aren't passing in an x vector to grepl . See ?grepl for more info.