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.

Example:

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.

Example:

bquote(x)
# x
bquote(.(x))
# [1] "y"