Solving the R error – ‘\u’ used without hex digits in character string starting ‘u’

If you’re seeing an R error message of ‘u’ used without hex digits in character string starting u then you’re probably a little confused. The R environment is generally pretty good at handling text encoding. But there are times when you have to give it a nudge in the right direction in order to ensure that it’s properly handling text fed into it. There are a few different issues that can create this error. But the crux of this error comes down to the fact that the R interpreter isn’t able to properly process text. Usually due to incorrect or unintended Unicode character attributes within the variable. Fixing the error just requires you to properly format the text. But the process of doing so will vary depending on the exact cause of the formatting problem.

What Does the Error Really Mean?

The error is caused by a perceived attempt at a Unicode formatted string. Unicode is an international encoding format that allows for a huge range of different languages and character sets. However, this does mean that Unicode isn’t quite as easy to work with as the American Standard Code for Information Interchange (ASCII).

One of the main points of difficulty with Unicode is that it uses special character options in a somewhat analogous way to HTML. But instead of using the forward slash seen in HTML, Unicode uses an escape sequence of \. And more specifically it uses a “u” followed by hexadecimal to signify Unicode.

The Unicode follows the u designator with a combination of values. Each code unit encodes for a specific, single, point and is the same size. With the numerical value specifying how it’ll be decoded. Unicode uses one to 12 octal digit variants or a hexadecimal digit pattern. However, this can create issues due to the fact that “\u” can show up in text for a variety of reasons. For example, an ASCII string might have “user” as a placeholder for a username and a “\” would transform that into “\username”. Thereby triggering the error.

This is especially common when working with data that requires specific formatting. For example, if you’re working with JSON datasets then you’ll typically need to use slashes as part of a newline character signal. If you’ve ever run into a problem with a / backslash being misinterpreted as HTML then you have an idea of the sort of issues that can pop up with Unicode. At the same time, Unicode is one of the best things to happen to string processing. It does complicate things in some instances. But it’s also why a character class or character sequence has so much flexibility.

There was a time when what you could see or write on digital systems was strictly limited by region. You’d typically need to work through larger-scale software updates on your operating system to add visual support for different linguistic character sets. But these days Unicode is an assumption and you can generally see text written in any language without needing to tinker with your operating system. Unicode is why a code point in a string can be an alphabetic character or, for example, kanji.

A Deeper Dive Into R’s String Handling

The concept can be seen with some simple code to create a string. Take a look at the following code.

ourString <- “Hello, \uworld”

The code assigns a value to ourString. Or, rather, it makes an attempt at it. The “\u” is interpreted as an attempt at unicode and the R interpreter exits out of the process. If you have control over the code you can just fix that by removing the slash. But of course that’s not always possible. Sometimes you’re not presented with a string literal that can be easily modified.

Fixing the Strings and the Errors

Thankfully this is generally a fairly easy issue to fix. The main point to consider is exactly why the error occurred in the first place. You might have it stemming from a failed attempt to use Unicode. In that case you could fix it with something like the following code.

ourString <- “Hello, \\uworld”
ourString <- str_replace_all(ourString, “\\\\u”, “\u002A”)

Note that we’re creating ourString with two backslashes in order to allow us to define it as such in R. In this example we use backslashes as escape characters to let the code match the target in ourString. Next, we replace the “\\u” with hex digit equal to a character string in Unicode. This of course assumes that the code we’re using is set up with character literals or other literal values that can’t simply be changed in the source code.

The ideal way to fix this problem is to simply keep it from happening in the first place. It’s generally a good idea to clean text that might contain a special character as it’s loaded. For example, you might try something like the following.

ourString <- “Hello, \\uworld”
ourString <- gsub(‘[^[:alnum:] ]’,”,ourString)

This basically uses a regular expression to remove anything except alphanumeric text from the raw string. The script essentially looks through the text and tries to match anything it finds with the alphanumeric character literals. If there’s no match then the characters are discarded.

Note that this problem can come up even within areas of R that you didn’t personally write. For example, it’s quite common for a path in Windows to have an “\u” in it. But you can generally just format a Windows path with / instead of \. Or use double or triple backslashes as escape characters.

Finally, keep in mind that some R processes might also store paths in config files. So if you’re starting an R script, IDE, etc and see the error? You might need to manually fix the paths to make sure that they’re using the correct backslash format. This is a fairly rare occurrence, but it’s something to keep in mind when all else fails.

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