title: Referring to a column in data frame with paste0 name
body: <p>I have a data frame with name paste0(i, "_SA") which is created in a loop.I want to print the 4th column but neither $ nor [,4] works. paste0(i, "_SA")[,4] gives error "incorrect number of dimensions" even though if I use this outside of the loop like US_SA[,4] it works. How do you refer to a column of paste0 named data frame?</p>