R automatically executes code following "unexpected symbol"-errors

Question

in recent months i realized a very annoying behaviour on both windows and unix R with R-Studio installations.

After an error, R is auto-executing every code it finds following a line producing an error(here: "unexpected symbol"). Here is an example code

vec1 <- c("Hallo", "World"

vec2 <- c(1,2,3)

print(vec2)

print(vec1)

In the first line:

vec1 <- c("Hallo", "World"

R is missing a closing ")". After erronously initializing it, this happens:

vec1 <- c("Hallo", "World"
+           
+ vec2 <- c(1,2,3)
Error: unexpected symbol in:
"          
vec2"
> 
> print(vec2)
Error in print(vec2) : object 'vec2' not found
> 
> print(vec1)
Error in print(vec1) : object 'vec1' not found
> 

R apparently does try to look for a closing bracket, finds one, gives the expected "Unexpected symbol"-error, but instead of stopping it does try to execute the next line (and everything else following) as well. Is this R- or R-Studio related and how can i stop that?

edit: I should clarify what the problem is, based on the comments. This behaviour is not intended, nor did i plan to include faulty lines to my code!

Sometimes one just forgets to add a bracket, or comma, or whatever, but still initializes such a line. Then - at least for me - R has this very annoying behaviour to then run through the entire code. Here is a real life example:

Somewhat later in the same situation, model objects were written over, which was very annoying.

So again, i dont want you to correct the code, i would like to learn why R behaves as descrined and how to stop it.

Answer 1

As per the customer support of R-Studio, this behaviour is related to R-Studio and can be stopped by unticking "Execute all lines in a statement" under Global Options -> Editing -> Execution. Sorry for bothering.

Answer 2

It sounds like you're expecting R to stop when it finds an error. After all, that's what traditional compiled languages like C and Java do. But R isn't a compiled language. Each line of code is interpreted in order. This is an inherent part of R and doesn't have anything to do with RStudio. In your example, it's really hard for R to figure out where the call to c() ends because you're missing the close parenthesis.

One RStudio feature that I find useful for preventing this specific type of error is the auto-formatter (CTRL-SHIFT-A). When formatting the code sample you provide, it becomes obvious that something's not right when you look at the indentation.

The code changes from this...

vec1 <- c("Hallo", "World"
vec2 <- c(1, 2, 3)
print(vec2)
print(vec1)

To this..

vec1 <- c("Hallo", "World"
          vec2 <- c(1, 2, 3)
          print(vec2)
          print(vec1)

The fact that the bottom three lines are indented so far to the right gives me a warning that I might have missed a closing parenthesis.

Generally

If your question is about broader error handling, you can often use a function to prevent R from continuing when it encounters an error. This won't work with your example since the parentheses are wrong, but it gives an answer to the broader question of when you can get R to stop upon encountering a problem.

Let's generate an error.

stop("This is an error")
print("The code keeps running!")

Notice how the second line runs after the error. Now let's wrap that code in a function.

demo_function <- function() {
  stop("This is an error")
  print("The code keeps running!")
}

demo_function()

The function throws an error and halts execution.

It's a good idea to put high-risk code inside of a function for exactly this reason. With the example you provided, R will throw an error as soon as you try to define the function, which might help you catch an error earlier in the development process.

Answer 3

You have to add some commas (' , ') and some parenthesis to your syntax, try with:

> vec1 <- c("Hello", "World")     
> vec2 <- c(1,2,3)
> print(vec2)
> print(vec1)

It should work.