In R, transform a character string into an operation

Question

If I have a character vector, how can I tell R to execute it as a command?

Simple example:

> a <- paste("2", "+", "3")

>a

>[1] "2 + 3"

I would like R to actually do 2+3, and not just print the content of "a".

Answer 1

The way to do it is

a <- paste("2", "+", "3")
eval(parse(text = a))

But, in general, it's not a great idea. There's usually a better way to do what you're trying to do.

> require(fortunes)
> fortune("parse")

If the answer is parse() you should usually rethink the question.
   -- Thomas Lumley
      R-help (February 2005)

There's lots of info on why eval(parse()) is considered a "bad practice" in the answers to What specifically are the dangers of eval(parse())?; in summary it is

• bug-prone

• harder to debug

• usually there's a more readable way to do whatever you're trying to do

• can pose a security risk

(though that last one probably doesn't apply for most R use cases)

Answer 2

eval(parse(text=paste("2", "+", "3")))