Error list object cannot be coerced to type double

In this article, we are looking towards the way to fix the “(list) object cannot be coerced to type ‘double” error in the R Programming language.

One of the most common errors that a programmer might face in R is:

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

This error might occur when we try to transform a list of multiple elements into the numeric without using the unlist() function.

When this error might occur:

Let’s create a list first:

Example:

Output:

Now we will convert the list into its numeric equivalent vector using as.numeric() function. The syntax of this function is given below:

Syntax: as.numeric(vect)

Parameter: vect: a vector of characters

Output:

Since we haven’t used the unlist() function that is why the compiler produced the error: “object that cannot be coerced to type a ‘double’ error message”.

How to Fix the Error:

This error can be fixed by first bundling the list into a vector using unlist() function and then passing it to the numeric() function. The syntax of the unlist() function is given below:

Syntax: unlist(list)

Parameter: list: It represents a list in R

Return Type: Returns a vector

Output:

Example:

To verify whether numeric_vector is of type numeric, we can use the class() function. The syntax of the class function is given below:

Syntax: class(x)

Parameter: Here, x represents a R object

Return Type: Returns the type of the passed object i.e, x (vector, list etc)

Output:

Also, to verify whether myList and numeric_vector contain an equal number of elements we can use a combination of sum() and lengths() function for myList and length() function for numeric_vector.

The syntax of the sum() function is given below:

Syntax: length(x)

Parameter: Here, x represents a R object like a vector or list

Return Type: Returns the number of elements present in x

Output:

This error occurs if you try to convert the elements of a list to numeric without converting the list to a vector using unlist().

You can solve this error by using the unlist() function before calling the numeric() function, for example,

num <- as.numeric(unlist(x))

This tutorial will go through the error and how to solve it with code examples.

Example

Consider the following example of a list containing strings.

x <- list(c("10", "38", "66", "101", "129", "185", "283", "374"))
x

[1] "10"  "38"  "66"  "101" "129" "185" "283" "374"

We want to convert the elements in the list to numeric. Let’s attempt to convert the elements using as.numeric().

x_num <- as.numeric(x)

Let’s run the code to see what happens:

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

The error occurs because we cannot use a list as an argument to the numeric() function. We can verify the object x is a list using the class() function:

class(x)

[1] "list"

Solution

The unlist function converts a list to a vector. The as.numeric() function accepts vector as an argument. We can use the unlist() function to solve this error. Let’s look at the revised code:

num <- as.numeric(unlist(x))
num

Let’s run the code to see the result:

[1]  10  38  66 101 129 185 283 374

We can verify that num is a vector of numeric values:

class(num)

[1] "numeric"

Summary

Congratulations on reading to the end of this tutorial!

For further reading on R related errors, go to the articles: 

• How to Solve R Error in lm.fit: na/nan/inf
• How to Solve R Error in apply: dim(X) must have a positive length
• How to Solve R Error in eval(predvars, data, env): object not found

Go to the online courses page on R to learn more about coding in R for data science and machine learning.

Have fun and happy researching!

Error: Coerce List Object to Type Double in R (2 Examples)

In this tutorial you’ll learn how to convert a list to a numeric vector in R.

Table of contents:

Here’s how to do it!

Creation of Example Data

As a first step, we have to create some data that we can use in the examples later on:

my_list Example 1: Reproducing Error: (list) object cannot be coerced to type ‘double

This Section illustrates a typical error message, when lists are converted to vectors or arrays. Have a look at the following R code:

as.numeric(my_list) # Wrong R code # Error: (list) object cannot be coerced to type ‘double’

As you can see, the RStudio console returns the error message: (list) object cannot be coerced to type ‘double’

The reason is that we cannot simply apply the as.numeric function to a list containing multiple list elements.

Next, I’ll explain how to fix this error. So keep on reading!

Example 2: Appropriate R Code for Conversion of List to Numeric Vector

Example 2 explains how to adequately convert a list to a numeric vector in R. Have a look at the following R code:

as.numeric(unlist(my_list)) # Apply unlist & as.numeric # 1 2 3 5 10 11 12 13 14 15

As you have seen, we used a combination of the unlist and as.numeric functions, i.e. first we are converting our list to a vector and then we convert this vector to numeric. Works smoothly!

Video & Further Resources

Do you need further info on the R programming syntax of this article? Then you might want to have a look at the following video of my YouTube channel. In the video tutorial, I show the examples of this article in RStudio.

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Additionally, I can recommend to read the other tutorials of my website.

In this R programming tutorial you learned how to convert lists to arrays. In case you have additional comments and/or questions, don’t hesitate to let me know in the comments section.

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