How to Solve R Error in parse(text): unexpected symbol

This error typically occurs if you have a string starting with a number or if a hyphen is in the wrong place.

To solve this error you can change the string so that it does not start with a number.

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

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Example

Let’s look at an example of a string, which we want to parse into an R expression:

str <- "xyz01-3lf"
parse(text=str)

Error in parse(text = str) : <text>:1:8: unexpected symbol
1: xyz01-3lf
           ^

We raise the error because R interprets the hyphen as the arithmetic operator for subtraction. The R cannot evaluate this as an expression therefore we cannot prase the string to an expression.

Solution

We can solve this error by removing the hyphen from the string. Let’s look at the revised code:

str <- "xyz013lf"
parse(text=str)

Let’s run the code to see the result:

expression(xyz013lf)

We can also substitute the hyphen for an underscore using gsub. Let’s look at the revised code:

parse(text=gsub('-', '_', str))

Let’s run the code to get the result:

expression(xyz01_3lf)

We can also put the string in backticks. Let’s look at the revised code:

str <- "xyz01-'3lf'"
parse(text=str)

Let’s run the code to see the result:

expression(`xyz01-3lf`)

Example

Let’s look at another example of a string starting with a number:

str <- "4xx Error"
parse(text=str)

Let’s run the code to see what happens:

Error in parse(text = str) : <text>:1:2: unexpected symbol
1: 4xx
     ^

The error occurs because the string starts with a number.

Solution

We can solve this error by wrapping the string in backticks. Let’s look at the revised code:

str <- "'4xx Error'"
parse(text=str)

Let’s run the code to get the result:

expression('4xx Error')

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: plot.window(…): need finite ‘ylim’ values
• How to Solve R Error: non-numeric argument to binary operator
• How to Solve R Error model.frame.default: ‘data’ must be a data.frame, environment, or list

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Have fun and happy researching!