title: compare columns of groups dataframe for equality
body: <p>My goal her is to compare a string or numeric among a group grouped by ID. So if for example var1 both were "NORMAL" a new column would say TRUE or FALSE. I know I can <code>summarise_all()</code> but I need it to be new column for another project. Also I would like this comparison to work for a numeric as well. All have to be exactly the same in the column of choice. Some of the groups have more than 2 members.</p>
  
  <pre><code>df &lt;- structure(list(ID = c("A1.1234567", "A1.12345"), 
                   var1 = c("NORMAL", "NORMAL"), 
                   var2 = c("NORMAL", "NORMAL"), 
                   var3 = c("NORMAL", "NORMAL"), 
                   var4 = c("NORMAL", "NORMAL"), 
                   var5 = c("NORMAL", "NORMAL"), 
                   var6 = c("NORMAL", "NORMAL"), 
                   var7 = c("25", "25"), 
                   var8 = c("6, 9)),
  
              .Names = c("ID", "var1", "var2", "var3", "var4", "var5", "var6", "var7", "var8"), 
              class = "data.frame", row.names = c(NA, -2L))
  </code></pre>
  
  <p>I want it to look like</p>
  
  <pre><code>         ID   var1   var2   var3   var4   var5   var6 var7 var8 var7.true va8.true
  A1.1234567 NORMAL NORMAL NORMAL NORMAL NORMAL NORMAL  25    6    TRUE   FALSE
  A1.1234567 NORMAL NORMAL NORMAL NORMAL NORMAL NORMAL  25    9    TRUE   FALSE
  </code></pre>
  
  <p>My only idea was to mutate it but I cant seem to compare them correctly</p>