title: How to avoid duplicate key error in swift when iterating over a dictionary
body: <p>I'm practicing swift and I'm trying to iterate over a Dictionary to print the key, but it gives me a </p>
  
  <blockquote>
    <p>fatal error: Dictionary literal contains duplicate keys</p>
  </blockquote>
  
  <p>How can remove the error? </p>
  
  <pre><code>let people = ["age":14, "age":15, "age":75, "age":43, "age":103, "age":87, "age":12]
  for (key, value) in people {
      print(value)
  }
  </code></pre>