title: Not sure why I am getting "Warning: Each child in an array or iterator should have a unique "key" prop."
body: <p>I am getting this error and I am not sure the other solutions I am finding are applicable. I think this error is occurring because I take the prop and extract the first array from "results" when mapping but I am not sure a better way to achieve this. Please let me know what a better practice for this could be. I am currently trying to test my searchbox but I cannot due to this error.</p>
  
  <pre><code>import React, { Component } from 'react';
  import CardList from './components/CardList';
  import './App.css';
  import SearchBox from './components/SearchBox';
  import {movies} from './movies';
  
  class App extends Component {
    constructor() {
      super()
      this.state = {
        movies: movies,
        searchfield: ''
      }
    }
  
    onSearchChange(event) {
      console.log(event.target.value);
    }
  
    render() {
      return (
        &lt;div className='tc'&gt;
          &lt;h1 className='f1'&gt;Now Playing: &lt;/h1&gt;
          &lt;SearchBox searchChange={this.onSearchChange}/&gt;
          &lt;CardList movies={this.state.movies}/&gt;
        &lt;/div&gt;
      );
    }
  }
  
  export default App;
  
  import React from 'react';
  import Card from './card/Card';
  
  const CardList = ({movies}) =&gt; {
  
      const results = movies[0].results;
  
      return (
          &lt;div&gt;
              {
                  results.map((user, i) =&gt; {
                      return (
                          &lt;Card 
                              poster={results[i].poster_path} 
                              title={results[i].title} 
                              summary={results[i].overview} 
                          /&gt;
                      );
                  })
              }
          &lt;/div&gt;
      );
  }
  
  export default CardList;
  
  export const movies = [
          {
              results: [
                  {
                      vote_count: 726,
                      id: 439079,
                      video: false,
                      vote_average: 5.9,
                      title: "The Nun",
                      popularity: 164.352,
                      poster_path: "/sFC1ElvoKGdHJIWRpNB3xWJ9lJA.jpg",
                      original_language: "en",
                      original_title: "The Nun",
                      genre_ids: [
                          27,
                          9648,
                          53
                      ],
                      backdrop_path: "/fgsHxz21B27hOOqQBiw9L6yWcM7.jpg",
                      adult: false,
                      overview: "When a young nun at a cloistered abbey in Romania takes her own life, a priest with a haunted past and a novitiate on the threshold of her final vows are sent by the Vatican to investigate. Together they uncover the order’s unholy secret. Risking not only their lives but their faith and their very souls, they confront a malevolent force in the form of the same demonic nun that first terrorized audiences in “The Conjuring 2,” as the abbey becomes a horrific battleground between the living and the damned.",
                      release_date: "2018-09-05"
                  },  
                  {
                      vote_count: 163,
                      id: 489999,
                      video: false,
                      vote_average: 7.6,
                      title: "Searching",
                      popularity: 33.883,
                      poster_path: "/9N0T3BaHZNdUCcMZQIM3yMUFwEh.jpg",
                      original_language: "en",
                      original_title: "Searching",
                      genre_ids: [
                          18,
                          53
                      ],
                      backdrop_path: "/qu2IPnFyDztlUOYhCkPptXP1vnv.jpg",
                      adult: false,
                      overview: "After his 16-year-old daughter goes missing, a desperate father breaks into her laptop to look for clues to find her. A thriller that unfolds entirely on computer screens.",
                      release_date: "2018-08-24"
                  },
  
                  {
                      vote_count: 349,
                      id: 346910,
                      video: false,
                      vote_average: 5.5,
                      title: "The Predator",
                      popularity: 154.329,
                      poster_path: "/wMq9kQXTeQCHUZOG4fAe5cAxyUA.jpg",
                      original_language: "en",
                      original_title: "The Predator",
                      genre_ids: [
                          27,
                          878,
                          28,
                          35
                      ],
                      backdrop_path: "/f4E0ocYeToEuXvczZv6QArrMDJ.jpg",
                      adult: false,
                      overview: "From the outer reaches of space to the small-town streets of suburbia, the hunt comes home. Now, the universe’s most lethal hunters are stronger, smarter and deadlier than ever before, having genetically upgraded themselves with DNA from other species. When a young boy accidentally triggers their return to Earth, only a ragtag crew of ex-soldiers and a disgruntled science teacher can prevent the end of the human race.",
                      release_date: "2018-09-13"
                  }
              ]
          }   
      ]
  </code></pre>