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POTest for equality among all elements of a single vector
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  1. POTest for equality among all elements of a single vector
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    copied!<p>I'm trying to test whether all elements of a vector are equal to one another. The solutions I have come up with seem somewhat roundabout, both involving checking <code>length()</code>.</p> <pre><code>x &lt;- c(1, 2, 3, 4, 5, 6, 1) # FALSE y &lt;- rep(2, times = 7) # TRUE </code></pre> <p>With <code>unique()</code>:</p> <pre><code>length(unique(x)) == 1 length(unique(y)) == 1 </code></pre> <p>With <code>rle()</code>:</p> <pre><code>length(rle(x)$values) == 1 length(rle(y)$values) == 1 </code></pre> <p>A solution that would let me include a tolerance value for assessing 'equality' among elements would be ideal to avoid <a href="http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f" rel="noreferrer">FAQ 7.31</a> issues.</p> <p>Is there a built-in function for type of test that I have completely overlooked? <code>identical()</code> and <code>all.equal()</code> compare two R objects, so they won't work here.</p> <p><strong>Edit 1</strong></p> <p>Here are some benchmarking results. Using the code:</p> <pre><code>library(rbenchmark) John &lt;- function() all( abs(x - mean(x)) &lt; .Machine$double.eps ^ 0.5 ) DWin &lt;- function() {diff(range(x)) &lt; .Machine$double.eps ^ 0.5} zero_range &lt;- function() { if (length(x) == 1) return(TRUE) x &lt;- range(x) / mean(x) isTRUE(all.equal(x[1], x[2], tolerance = .Machine$double.eps ^ 0.5)) } x &lt;- runif(500000); benchmark(John(), DWin(), zero_range(), columns=c("test", "replications", "elapsed", "relative"), order="relative", replications = 10000) </code></pre> <p>With the results:</p> <pre><code> test replications elapsed relative 2 DWin() 10000 109.415 1.000000 3 zero_range() 10000 126.912 1.159914 1 John() 10000 208.463 1.905251 </code></pre> <p>So it looks like <code>diff(range(x)) &lt; .Machine$double.eps ^ 0.5</code> is fastest.</p>
 

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