R Error Message Cheat Sheet

An error shows up in red in your RStudio terminal. Here are some of the most common errors and how to fix them:

Error: object 'foo' not found

(Where foo is any name). You tried to access a variable that doesn’t exist. You might have

• misspelled the variable name
• incorrectly capitalized the variable name (R is case sensitive!)
• forgotten to run the line that defines the variable in the first place, or run into an error on that line.

Error: could not find function "foo"

(Where foo is any name). You tried to use a function (like foo(bar)) that doesn’t exist. You might have:

• misspelled the function name
• incorrectly capitalized the function name
• forgotten to load the library that provides this function. For example, before you use as.data.table, you have to load the data.table library with library("data.table").
• accidentally put a variable name before an open parentheses, perhaps meaning to perform multiplication. For instance, writing foo (bar + 1) when you mean foo * (bar + 1). R doesn’t treat these parentheses as implicit multiplication: it attempts to find a function called foo (which doesn’t exist).

Error: unexpected ')' in...

There is an extra end parenthesis in your line (it’s easy to lose track of these once they start getting nested). Count and make sure that you have one close parenthesis for each open parenthesis. (The same goes for unexpected ']', unexpected '}' and similar errors).

Error: unexpected symbol in...

The most common cause of this is forgetting a punctuation mark such as a comma: for example, foo(bar1 bar2) instead of foo(bar1, bar2). Error: unexpected numeric constant is similar: it just means the value after the missing punctuation is a number (for example, x 2 instead of x = 2).

+

You might see a + sign in the interpreter after you hit return. This means the previous statement is unfinished: it might have an open parenthesis that never closes, an open " or ' that is unmatched, or it could end with an operator like + or - that expects the line to continue afterwards. Hit the esc key to cancel this line, then find the problem with your previous line (count parentheses, and check your quotes) and fix it.