title: Clojure: IllegalArgumentException Key must be integer
body: <p>I have two lists:</p>
  
  <pre><code>(def xxa ["olp" "xyz"])
  (def xxb ["ulove" "alove" "holp" "sholp"])
  </code></pre>
  
  <p>and a function trying to get the elements of the 1st list that are parts of elements of the 2nd list:</p>
  
  <pre><code>(defn in-array
    [array1 array2]
    (for [s1 array1 :when (some #(.contains %1 s1) array2)] s1))
  </code></pre>
  
  <p>(in-array xxa xxb) should return ["olp"]</p>
  
  <p>but I get:</p>
  
  <pre><code>IllegalArgumentException Key must be integer  clojure.lang.APersistentVector.invoke
  </code></pre>
  
  <p>I don't understand what that means. Can someone gives me some light?</p>