title: Warning: Each Child in an Array or Iterator Should Have a Unique “Key” Prop
body: <p>When i map an array with Picker item i got the following warning:</p>
  
  <blockquote>
    <p>Each child in an array should have a unique "key" prop.</p>
  </blockquote>
  
  <p>Here is my code</p>
  
  <pre><code>var locationArray = [{"name":"canada","id":"2"},{"name":"sweden","id":"3"}];
  
  var Locations = locationArray.map(function(result) {
  return &lt;Picker.Item label={result.name} value={result.id} /&gt; ;
  });
  
  return (
      &lt;ScrollView contentContainerStyle={styles.contentContainer}&gt;
          &lt;View style={styles.container}&gt;
              &lt;Picker selectedValue={this.state.location} onValueChange={(location) =&gt; this.setState({location:location})} style={[styles.picker, {color: '#2E3740'}]}&gt;
                  {Locations}
              &lt;/Picker&gt;
          &lt;/View&gt;
      &lt;/ScrollView&gt;
  );
  </code></pre>