title: Error in Stratified sampling
body: <p>I used <code>SamplingStrata</code> package which includes <code>strata</code> function to select random samples. This selection is based on a field which has a unique ID and it is named as strata. Each of these IDs contains a minimum of 5 and maximum of 10 samples. You could see the below codes for selecting 3 samples from each strata and the error I receive. I am copying data elements below the R script. Please help out with the issue in error. Thank you. </p>
  
  <pre><code>#### R script and Data = samples
  stratasamples&lt;-strata(samples, stratanames = "TARGET_FID", size=3, method="srswor")
  
  
  ### Error 
  Error in if (method != "srswr" &amp; length(y) &lt; size[i]) { : 
    missing value where TRUE/FALSE needed
  
  ### Data elements. ### Strata = TARGET_FID. Samples = JOIN_FID 
  TARGET_FID  0   0  0  0  0  1  1  1  1  2 2 
  JOIN_FID    12 14 16 18 10 23 28 39 48 90 92
  </code></pre>