How to make grepl function specific?

Question

My data frame is shown as below. I need extract the data of a specific row according to the name of "geneID" column one by one. I use grepl function.

#Data frame:geneDf  
geneID=c("EGFR","Her2","PTENPP","PTEN")
patient1=c(12,23,56,23)
patient2=c(23,34,11,6)
patient3=c(56,44,32,45)
patient4=c(23,64,45,23)
geneDf=data.frame(patient1,patient2,patient3,patient4,geneID)

geneDf
  patient1 patient2 patient3 patient4 geneID
1       12       23       56       23   EGFR
2       23       34       44       64   Her2
3       56       11       32       45 PTENPP
4       23        6       45       23   PTEN

The first three rows work well.

targetGene<-subset(geneDf,grepl(geneDf$geneID[1],geneDf$geneID))
targetGene
  patient1 patient2 patient3 patient4 geneID
1       12       23       56       23   EGFR

When I extract the data of the 4th row, I get this:

targetGene<-subset(geneDf,grepl(geneDf$geneID[4],geneDf$geneID))
targetGene
  patient1 patient2 patient3 patient4 geneID
3       56       11       32       45 PTENPP
4       23        6       45       23   PTEN

It seems other data,in this case, the 3rd row of "geneID" column, which includes the content of the 4th row is picked up too. What's wrong with my command? How to make it only pick up the data of a certain row each time?

Answer 1

You may need word boundary i.e. \\b or use

subset(geneDf, grepl(paste0('^', geneID[4], '$'), geneID))
#  patient1 patient2 patient3 patient4 geneID
#4       23        6       45       23   PTEN

Or

subset(geneDf, grepl(paste0('\\b', geneID[4], '\\b'), geneID))
#   patient1 patient2 patient3 patient4 geneID
#4       23        6       45       23   PTEN

Answer 2

@akrun has answered your specific question, but if you are looking to create subsets of your data according to another variable, you may also be interested in the split function:

split(geneDf, geneDf$geneID)
## $EGFR
##   patient1 patient2 patient3 patient4 geneID
## 1       12       23       56       23   EGFR
## 
## $Her2
##   patient1 patient2 patient3 patient4 geneID
## 2       23       34       44       64   Her2
## 
## $PTEN
##   patient1 patient2 patient3 patient4 geneID
## 4       23        6       45       23   PTEN
## 
## $PTENPP
##   patient1 patient2 patient3 patient4 geneID
## 3       56       11       32       45 PTENPP
##