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POWhy is the terminology of labels and levels in factors so weird?
 

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  1. POWhy is the terminology of labels and levels in factors so weird?
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    <p>An example of a non-settable function would be <code>labels</code>. You can only set factor labels when they are created with the factor function. There is no <code>labels&lt;-</code> function. Not that 'labels' and 'levels' in factors make any sense....</p> <pre><code>&gt; fac &lt;- factor(1:3, labels=c("one", "two", "three")) &gt; fac [1] one two three Levels: one two three &gt; labels(fac) [1] "1" "2" "3" </code></pre> <p>OK, I asked for labels, which one might assume were as set by the factor call, but I get something quite ... what's the word, unintuitive? </p> <pre><code>&gt; levels(fac) [1] "one" "two" "three" </code></pre> <p>So it appears that setting labels is really setting levels.</p> <pre><code>&gt; fac &lt;- factor(1:3, levels=c("one", "two", "three")) &gt; levels(fac) [1] "one" "two" "three" </code></pre> <p>OK that is as expected. So what are labels when one sets levels?</p> <pre><code>&gt; fac &lt;- factor(1:3, levels=c("one", "two", "three"), labels=c("x","y", "z") ) &gt; labels(fac) [1] "1" "2" "3" &gt; levels(fac) [1] "x" "y" "z" </code></pre> <p>Effing weird, if you ask me. It would seem that 'labels' arguments for factor trump any 'levels' arguments for the specification of levels. Why should this be? Seems like a confused terminology. And why does <code>labels()</code> return what I would have imagined to be retrieved with as.character(as.numeric(fac))?</p> <p>(This was a tangential comment [labelled as such] in an earlier answer about assignment functions to which I was asked to move to a question. So here's your opportunity to enlighten me.)</p>
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    1. CONote that in both your second and third examples, `fac` or `str(fac)` would reveal that your factor is all `NA`s, because the `levels` specification you gave didn't match the values of `x` ...
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      1. USBen Bolker
 

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