title: Warning in xtfrm.data.frame(x) : cannot xtfrm data frames: error while ordering a dataframe numerically in R
body: <p>I started learning R a couple of weeks ago, so I'm still very very new to R coding; I was trying to order a dataframe numerically, but on top of the ordered dataframe, resulted from the execution of the function order(nameofthedataframe), it appears &quot;Warning in xtfrm.data.frame(x) : cannot xtfrm data frames&quot;. Could please anyone tell me what did I do wrong?</p>
  <p>Thank you very much!</p>
  <p>Examples:</p>
  <pre><code>order(iris[,&quot;Petal.Width&quot;]) # this seems fine
  order(iris[,&quot;Petal.Width&quot;,drop=FALSE]) # warning
  order(iris[,c(&quot;Petal.Width&quot;,&quot;Sepal.Width&quot;)]) # warning
  </code></pre>
  <p>R version 4.1.0</p>