Standard and Non Standard Evaluation in R
Standard Evaluation in R:
In standard evaluation, the code you type in is taken to be variable names, functions, names, operators, and even numeric literal values. String values or literals need extra marks.
d <- data.frame(x = 1, y = 2) x <- "y"
Non Standard Evaluation in R:
In non-standard evaluation, the roles are reversed. Names are treated as literal string values unless extra marks are added.
bquote(x) # x bquote(.(x)) #  "y"