What does "Error: object '<myvariable>' not found" mean?

Question

I got the error message:

Error: object 'x' not found

Or a more complex version like

Error in mean(x) : error in evaluating the argument 'x' in selecting a method for function 'mean': Error: object 'x' not found

What does this mean?

Answer 1

The error means that R could not find the variable mentioned in the error message.

The easiest way to reproduce the error is to type the name of a variable that doesn't exist. (If you've defined x already, use a different variable name.)

x
## Error: object 'x' not found

The more complex version of the error has the same cause: calling a function when x does not exist.

mean(x)
## Error in mean(x) : 
##   error in evaluating the argument 'x' in selecting a method for function 'mean': Error: object 'x' not found

Once the variable has been defined, the error will not occur.

x <- 1:5
x
## [1] 1 2 3 4 5     
mean(x)
## [1] 3

---

You can check to see if a variable exists using ls or exists.

ls()        # lists all the variables that have been defined
exists("x") # returns TRUE or FALSE, depending upon whether x has been defined.

---

Errors like this can occur when you are using non-standard evaluation. For example, when using subset, the error will occur if a column name is not present in the data frame to subset.

d <- data.frame(a = rnorm(5))
subset(d, b > 0)
## Error in eval(expr, envir, enclos) : object 'b' not found

---

The error can also occur if you use custom evaluation.

get("var", "package:stats") #returns the var function
get("var", "package:utils")
## Error in get("var", "package:utils") : object 'var' not found

In the second case, the var function cannot be found when R looks in the utils package's environment because utils is further down the search list than stats.

---

In more advanced use cases, you may wish to read:

• The Scope section of the CRAN manual Intro to R and demo(scoping)
• The Non-standard evaluation chapter of Advanced R