Using Subscripts and Superscripts in R console

问题

This is more for curiosity, but is it possible to write subscripts in R console and, if so, how would I do that?

I am using a Mac and
typically code in RStudio

Although assignment statements work with Greek letters, e.g. μ,σ, but I can't get superscripts or subscripts working. I'd like to write an assign statement such as σ² <- 1 and have it be recognized. In particular, typing that last command I get the following error message

Error: unexpected input in "σ�"

回答1:

You can, but you shouldn't; names that don't stick to R's standards cause problems eventually.

The rules, from ?Quotes:

Names and Identifiers

Identifiers consist of a sequence of letters, digits, the period (.) and the underscore. They must not start with a digit nor underscore, nor with a period followed by a digit. Reserved words are not valid identifiers.

The definition of a letter depends on the current locale, but only ASCII digits are considered to be digits.

Such identifiers are also known as syntactic names and may be used directly in R code. Almost always, other names can be used provided they are quoted. The preferred quote is the backtick (`), and deparse will normally use it, but under many circumstances single or double quotes can be used (as a character constant will often be converted to a name). One place where backticks may be essential is to delimit variable names in formulae: see formula.

If you still want to break the rules, there are a couple ways. You can use assign:

> assign('σ²', 47)
> `σ²`
[1] 47
> σ²
Error: unexpected input in "σ�"

Notice, however, that dependent on your locale, you may need to wrap σ² in backticks to call it successfully.

You can also wrap it in backticks to assign:

> `σ²` <- 47
> `σ²`
[1] 47
> σ²
Error: unexpected input in "σ�"

As you can see, you'll still likely need to wrap any calls in backticks (especially if you want your code to be faintly portable).

That said, this is all a REALLY, REALLY BAD IDEA.

Your variable names will be hard to type;
Your code will likely not be portable;
You stand a very good chance of causing errors in more complicated functions later (e.g. NSE functions would be very unpredictable);
It's a good way to do really stupid things:

> `+` <- `-`
> 1 + 1
[1] 0

The rules are there for a reason. Unless you've got a really good reason to break them, don't.

Addendum

If you just want to use symbolic expressions as strings, encodeString and format are both useful:

> encodeString('σ²')
[1] "σ²"
> format('σ²')
[1] "σ²"

See their help pages for more specifics, but it's generally possible to use any symbol (even emoji!) in a string, if you're a little careful what functions you pass it to.

💻💻💻💻💻💻💻

回答2:

I am using windows so maybe this doesn't work on a mac. The following code allows superscript for me.

    > assign("σ²", 3)
    > σ²
    [1] 3

Hope this helps :)

来源：https://stackoverflow.com/questions/35398354/using-subscripts-and-superscripts-in-r-console

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