r - Calling objects as column name in R Combine Function

Question

I have an array(pstype) whose elements are column names for another data frame, i would like to call a column name[Array Element] one by one from that array by attaching ".x" and ".y" with it and put those columns in a new data frame(new_df):

eg:

pstype<-c("eid","esal","exp")

df2:
eid esal.x  exp.x   esal.y  exp.y
2    4       1       4       1
3    4       2       4       2
4    4       3       4       3
5    3       3       3       3

df1:
eid
2
3
4
5

This is what i am trying to do:

for(i in 1:length(pstype)){

  xpstype<-paste(pstype[i],".x",sep="")
  ypstype<-paste(pstype[i],".y",sep="")

  new_df<-merge(df1,df2[,c("eid",xpstype,ypstype)],by="eid")

}

The error that i'm getting is: by passing an object to c("eid",xpstype,ypstype)

Error: undefined columns selected