title: R - argument is not numeric or logical: returning NA
body: <p>I am trying to get the mean of the data read from an excel sheet.</p>
  
  <pre><code>library(readxl)
  URL &lt;- "C:/Users/user/Documents/R/test.xlsx"
  pivot &lt;- read_excel(URL,sheet=2)
  pivot
  mean(pivot$Experimental)
  </code></pre>
  
  <p>Data in excel below. This data is shown on the console window when executing the code above.</p>
  
  <pre><code> Experimental   Comparison
     -0.255      -0.324
     -0.213      -0.185
     -0.190      -0.299
     -0.185      -0.144
     -0.045      -0.027
     -0.025      -0.039
     -0.015      -0.264
      0.003      -0.077
      0.015      -0.017
      0.020      -0.169
      0.023      -0.096
      0.040      -0.330
      0.040      -0.346
      0.050      -0.191
      0.055      -0.128
      0.058      -0.182  
  </code></pre>
  
  <p>I am getting the below warning message and result of the mean function is NA.</p>
  
  <pre><code>Warning message:
  In mean.default(pivot$Experimental) :
    argument is not numeric or logical: returning NA
  </code></pre>