title: R cooccur package error when plotting data
body: <p>I'm having trouble with the cooccur package. After creating the cooccur object, I'm trying to plot it to obtain a heatmap of positive/negative co-occurrence. This should be simple- the code in the example is just "plot(<em>cooccur_object</em>)" but it's throwing an error: <strong>Error in zero_range(from) : x must be length 1 or 2</strong>. I've included reproducible code, and any ideas are welcome. The error seems to depend on the numbers themselves, as the example code works perfectly with the "finches" data set and only throws errors occasionally when the numbers are randomly generated. The reproducible code below throws the error, but if you change the seed it'll sometimes run and sometimes won't. Any thoughts?</p>
  
  <pre><code>set.seed(13532)
  a &lt;- rnorm(100)
  a[a&gt;0] &lt;- 1
  a[a&lt;0] &lt;- 0
  a
  b &lt;- matrix(a, ncol = 10)
  df &lt;- as.data.frame(b)
  names(df) &lt;- c(paste("Subject", 1:10))
  row.names(df) &lt;- c(paste("Disease", LETTERS[1:10]))
  df
  
  library(cooccur)
  cooc &lt;- cooccur(df)
  plot(cooc)
  summary(cooc)
  </code></pre>