[R] quote a column of a dataframe by its name

[Jie]

Dear All,

I have a question, suppose X is a dataframe, with column names as
"x1", "x2", "x3", ..... And I would like to use the i-th column by X[,'xi'].
But it seems the single quote and double quote are different.
So if I run X[, names(X)[i]], it has some error.
Please use the below example code

X = matrix(rnorm(50),ncol = 5)
X = data.frame(X)
names(X)=c("x1","x2","x3","x4","x5")

#pick the 4-th column
X[,'x4']  #working
X[,names(X)[4]]  # not working , so how to modify this line?

names(X)[4] #  returns "x4"
sQuote(names(X)[4])  # returns "'x4'"


Best,