One common error you may encounter in R is:

Error: (list) object cannot be coerced to type 'double'

This error occurs when you attempt to convert a list of multiple elements to numeric without first using the **unlist()** function.

This tutorial shares the exact steps you can use to troubleshoot this error.

**How to Reproduce the Error**

The following code attempts to convert a list of multiple elements to numeric:

#create list x <- list(1:5, 6:9, 7) #display list x [[1]] [1] 1 2 3 4 5 [[2]] [1] 6 7 8 9 [[3]] [1] 7 #attempt to convert list to numeric x_num <- as.numeric(x) Error: (list) object cannot be coerced to type 'double'

Since we didn’t use the **unlist()** function, we received the **(list) object cannot be coerced to type ‘double’** error message.

**How to Fix the Error**

To convert the list to numeric, we need to ensure that we use the **unlist()** function:

#create list x <- list(1:5, 6:9, 7) #convert list to numeric x_num <- as.numeric(unlist(x)) #display numeric values x_num [1] 1 2 3 4 5 6 7 8 9 7

We can use the **class()** function to verify that x_num is actually a vector of numeric values:

#verify that x_num is numeric class(x_num) [1] "numeric"

We can also verify that the original list and the numeric list have the same number of elements:

#display total number of elements in original list sum(lengths(x)) [1] 10 #display total number of elements in numeric list length(x_num) [1] 10

We can see that the two lengths match.

**Additional Resources**

The following tutorials explain how to troubleshoot other common errors in R:

How to Fix in R: names do not match previous names

How to Fix in R: contrasts can be applied only to factors with 2 or more levels

How to Fix in R: longer object length is not a multiple of shorter object length