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    <p>The <code>labels</code> function sounds like the perfect fit for getting the labels of a factor.</p> <p>...but the <code>labels</code> function has nothing to do with factors! It is used as a generic way of getting something to "label" an object. For atomic vectors, this would be the names. But if there are no names, the <code>labels</code> function returns the element indices coerced to strings - something like <code>as.character(seq_along(x))</code>.</p> <p>...So that's what your seeing when you try labels on a factor. The factor is an integer vector without any names, but with a <code>levels</code> attribute.</p> <p>A factor has no labels. It only has levels. The <code>labels</code> argument to <code>factor</code> is just a way to be able to give a set of strings but produce another set of strings as the levels... But to confuse things further, the <code>dput</code> function prints the <code>levels</code> attributes as <code>.Label</code>! I think that is a legacy thing...</p> <pre><code># Translate lower case letters to upper case. f &lt;- factor(letters[2:4], letters[1:3], LETTERS[1:3]) dput(f) #structure(c(2L, 3L, NA), .Label = c("A", "B", "C"), class = "factor") attributes(f) #$levels #[1] "A" "B" "C" # #$class #[1] "factor" </code></pre> <p>However, since <code>labels</code> is a generic function, it would probably be a good idea to define <code>labels.factor</code> as follows (currently there is none). Perhaps something for R core to consider?</p> <pre><code>labels.factor &lt;- function(x, ...) as.character(x) </code></pre>
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    1. POWhy is the terminology of labels and levels in factors so weird?
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    1. COAlmost, with one small correction. If there are no names, `labels` returns **sequence numbers** (`seq_along(x)`) coerced to strings ...
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    2. CO@Ben Bolker, Yep your're right - I shouldn't try stuff like `labels(1:3)` :-). I updated the answer.
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    3. COThree problems with that answer. (1) With factors, `labels` does _not_ return what one would get with as.character(fac) which is how I would have interpreted your statement "returns values coerced to strings". (2) Can you explain why the `labels` function does not return what was set by the "labels" argument to `factor`? (3) And why 'labels' trumps 'levels'?
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