D3 Examples - Film Flowers, Single Update Starter

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<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <script src='https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.13.1/lodash.js'></script>
  <link href='https://fonts.googleapis.com/css?family=Libre+Baskerville:400,700' rel='stylesheet' type='text/css'>
  
  <style>
    svg {
      width: 600px;
      height: 20000px;
    }
  </style>
</head>
​
<body>
  <svg></svg>
  
  <script>
    const width = 600;
    const height = 600;
    
    const petalPaths = [[
        'M0,0',
      "C50,50 50,100 0,100",
      "C-50,100 -50,50 0,0"
    ],
    [
            'M-35,0',
      'C-25,25 25,25 35,0',
      'C50,25 25,75 0,100',
      'C-25,75 -50,25 -35,0'
    ],
    [
      'M0,0',
      'C50,40 50,70 20,100',
      'L0,85',
      'L-20,100',
      'C-50,70 -50,40 0,0'
    ],
    [
      'M0,0',
      'C50,25 50,75 0,100',
      'C-50,75 -50,25 0,0'
    ]];
    
    // instantiate scales and petal path lookup
    const sizeScale = d3.scaleLinear()
        .range([0.1, 1]);
    const numPetalsScale = d3.scaleQuantize()
        .range(_.range(5, 10));
    const pathLookup = {
      G: petalPaths[0],
      PG: petalPaths[1],
      'PG-13': petalPaths[2],
      R: petalPaths[3],
    };
    
    // grab svg
    const svg = d3.select(' svg');
    
    /*****************************************************
    ** get movie data
    ******************************************************/
    
    d3.json('movies.json', function(movies) {
      movies = _.map(movies, movie => {
        return {
          rating: ++movie.imdbRating,
          votes: parseInt(movie.imdbVotes.replace(/\,/g, '')),
          year: ++movie.Year,
          title: movie.Title,
          pg: movie.Rated,
        }
      });
      
      // 1. set domain for scales
      // size scale = rating
      // number of petals scale = number of votes
      const sizeExtent = d3.extent(movies, d => d.rating);
      const numPetalsExtent = d3.extent(movies, d => d.votes);
      // set domain on scales
      sizeScale.domain(sizeExtent);
      numPetalsScale.domain(numPetalsExtent);
      
      // function that calculates data for the petals
      // and draws flower with enter-update-exit
     
        const createPetalData = (movie) => {
      const numPetals = numPetalsScale(movie.votes);
      return _.times(numPetals, (i) => {
        // 1. rotation of the petal
        const rotate = (i / numPetals) * 360;
        // 2. path of petal (pg)
        // 3. size of petals (IMDB ratings)
        return {
          rotate,
          path: pathLookup[movie.pg],
          scale: sizeScale(movie.rating)
        }
      });
    }
        
        const transition = d3.transition().duration(1000);
        // 3. set data and enter-update-exit
        
        const groups = svg.selectAll('g').data(movies).enter().append('g').attr('transform', (d, i) => 
          `translate(100, ${200 * i+ 20})`);
        groups.append('text').attr('text-anchor', 'right').text(d => d.title);
         let petals = groups.selectAll('path')
        .data((d) => createPetalData(d));
        
        // exit
        petals.exit().transition(transition).attr('transform', d => `translate(100,100)rotate(0)scale(${0})`).remove();
        
        // enter
        const enter = petals.enter().append('path')
        .attr('transform', d => `translate(100,100)rotate(${d.rotate})scale(${0})`)
        
        // enter and update
        petals = petals.merge(enter)
        .transition(transition)
        .attr('transform', d => `translate(100,100)rotate(${d.rotate})scale(${d.scale})`)
        .attr('d', d => d.path)
        .attr('fill', (d, i) => d3.interpolateRainbow(i / d.path.length));
      
            
    });
    
  </script>
</body>
​
    