What is the difference between aes and aes_string (ggplot2) in R

Question

With missing background in informatics I have difficulties to understand the differences between aes and aes_string in ggplot2 and its implications

Answer 1

aes saves you some typing as you don't need the quotes. That is all. You are of course free to always use aes_string. You should use aes_string if you want to pass the variable names programmatically.

Internally aes uses match.call for the non-standard evaluation. Here is a simple example for illustration:

fun <- function(x, y) as.list(match.call())
str(fun(a, b))
#List of 3
# $  : symbol fun
# $ x: symbol a
# $ y: symbol b

For comparison:

library(ggplot2)
str(aes(x = a, y = b))
#List of 2
# $ x: symbol a
# $ y: symbol b

The symbols are evaluated at a later stage.

aes_string uses parse to achieve the same:

str(aes_string(x = "a", y = "b"))
#List of 2
# $ x: symbol a
# $ y: symbol b