title: Trying to look at interaction plot in emmeans - Error caused by missing argument in emmip?
body: <p>I'm following the vignette for examining interactions using emmeans here
  <a href="https://cran.r-project.org/web/packages/emmeans/vignettes/interactions.html" rel="nofollow noreferrer">https://cran.r-project.org/web/packages/emmeans/vignettes/interactions.html</a></p>
  
  <p>But I'm using my own dataset (all.det) - which does have significant interactions.
  all.det contains 1621 observations of 12 variables, 3 of which are factors. 
  I did try to create a re-producible example, but haven't figured out how to create one with all interactions significant. So I'm hoping this description will be enough for someone to point out where I am going wrong.</p>
  
  <p>I am using</p>
  
  <pre><code>library(data.table)
  library(car)
  library(emmeans)
  </code></pre>
  
  <p>I run an anova using this code</p>
  
  <p>DistanceKm is a numeric and Method, IDGroup and Sightability are factors.</p>
  
  <pre><code>model = lm(DistanceKm ~ Method * IDGroup * Sightability,
             data=all.det[(IDGroup == "Whale" | IDGroup == "Dolphin")
                          &amp; DistanceKm &lt;=5])
  Anova(model, type="II")
  </code></pre>
  
  <p>All the interactions are significant, so I follow this up with an interaction plot as advised in the vignette</p>
  
  <pre><code>emmip(model, Method ~ Sightability | IDGroup)
  </code></pre>
  
  <p>But I get these errors</p>
  
  <pre><code>Error in if (!all(chk == tbl)) stop("Data appear to be randomized -- ",  : 
    missing value where TRUE/FALSE needed
  Error in ref_grid(object, ...) : 
    Perhaps a 'data' or 'params' argument is needed
  </code></pre>
  
  <p>I did try to create a subset of my data</p>
  
  <pre><code>sub=all.det[(IDGroup == "Whale" | IDGroup == "Dolphin") &amp; DistanceKm &lt;=5]
  </code></pre>
  
  <p>And then re-ran the model, followed with an Anova</p>
  
  <pre><code>model=lm(DistanceKm ~ Method * IDGroup * Sightability, data=sub)
  Anova(model, type="II")
  </code></pre>
  
  <p>I get the same Anova results (as expected), but now I'm also able to produce the interaction plot without errors.</p>
  
  <pre><code>emmip(model, Method ~ Sightability | IDGroup)
  </code></pre>
  
  <p>I just get a single warning instead about a missing value</p>
  
  <p>Am I missing something when calling emmip?</p>