<div id="app">
  <select v-model="selected">
    <option v-for="option in options" v-bind:value="option.value">
      {{ option.text }}
    </option>
  </select>
  
  <svg viewBox="0 0 400 400">
    <!--xaxis -->
    <g targetVal="targetVal"  class="xaxis">
      <line x1="0" y1="1" x2="350" y2="1"/>
      <g v-for="(select, index) in targetVal">
        <line y1="0" y2="7" v-bind="{ 'x1':index*10, 'x2':index*10 }"/>
        <text v-if="index % 5 === 0" v-bind="{ 'x':index*10, 'y':20 }">{{ index }}</text>
      </g>
    </g>
    
    <!--yaxis -->
    <g class="yaxis">
      <line x1="0" y1="1" :x2="getMax" y2="1"/>
      <g v-for="n in getMaxRange">
        <line y1="0" y2="7" v-bind="{ 'x1':n*10, 'x2':n*10 }"/>
        <text v-if="n % 5 === 0" v-bind="{ 'x':getMax-(n*10)-5, 'y':20 }">{{ n }}</text>
      </g>
    </g>
    
  <!-- bars -->
    <g v-for="(select, index) in targetVal" class="bars">
      <rect v-bind="{ 'x':index*10+20, 'y':getMax-select*10 }" width="10" :height="select*10"/>
    </g>
    
  </svg> 
</div>

body {
  font-family: 'Mada', sans-serif;
  background: #222;
}

#app {
  text-align: center;
  max-width: 400px;
  margin: 30px auto;
  display: table;
}

span {
  color: white;
}

svg {
  width: 400px;
  text {
    fill: grey;
    font-family: 'Mada', sans-serif;
  }
}

line {
  stroke: #555;
  stroke-width: 2px;
}

select {
  font-family: 'Mada', sans-serif;
  background: #444;
  color: #ccc;
  border: 0;
  width: 200px;
  margin: 0 0 25px;
  outline: 0;
  cursor: pointer;
  height: 35px;
  option {
    font-family: 'Mada', sans-serif;
  }
}

.xaxis {
  transform: translate(20px, 370px);
}

.yaxis {
  transform: translate(20px, 0px) rotate(90deg);
}

$amt : 350px;
$max: 40;
$color: 300/$max;

@for $i from 1 through $max {
  .bars:nth-child(#{$i}) rect {
    fill: hsl(($i - 10)*($color*1.25), ($i - 1)*$color, 40%);
  }
}

new Vue({
  el: '#app',
  data() {
    return {
      selected: [25, 37, 15, 13, 25, 30, 11, 17, 35, 10, 25, 15, 5, 27, 15, 13, 25, 36, 15, 14, 35, 10, 14, 15, 35, 17, 12, 13, 25, 30, 14, 17, 35, 10, 25, 15],
      targetVal: [25, 37, 15, 13, 25, 30, 11, 17, 35, 10, 25, 15, 5, 27, 15, 13, 25, 36, 15, 14, 35, 10, 14, 15, 35, 17, 12, 13, 25, 30, 14, 17, 35, 10, 25, 15],
      options: [
      { text: 'First Dataset', value: [25, 37, 15, 13, 25, 30, 11, 17, 35, 10, 25, 15, 5, 27, 15, 13, 25, 36, 15, 14, 35, 10, 14, 15, 35, 17, 12, 13, 25, 30, 14, 17, 35, 10, 25, 15] },
      { text: 'Second Dataset', value: [13, 25, 30, 11, 17, 35, 10, 25, 15, 5, 27, 15, 13, 25, 36, 15, 14, 35, 10, 14, 15, 35, 17, 12, 13, 25, 30, 14, 17, 35, 10, 25, 15, 25, 37, 15] },
      { text: 'Third Dataset', value: [35, 10, 25, 15, 5, 27, 15, 13, 25, 36, 15, 14, 35, 10, 14, 15, 35, 17, 12, 13, 25, 30, 14, 17, 35, 10, 25, 15, 25, 37, 15, 13, 25, 30, 11, 17] }
     ]
    }
  },
  computed: {
    getMax() {
      return Math.max.apply( Math, this.selected )*10;
    },
    getMaxRange() {
      let maxi = Math.max.apply( Math, this.selected );
      return _.range(maxi);
    }
  },
  watch: {
    selected(newValue, oldValue) {
      // Create a dummy object that will get updated by GSAP
      var tweenedData = {}      

      // Update function that is invoked on each tween step 
      // we use this to push the data
      var update = function() {
        let obj = Object.values(tweenedData);
        obj.pop();
        this.targetVal = obj;
      }

      // Create an object to hold the source data to be tweened and the
      // function pointer for update events
      var tweenSourceData = { onUpdate: update, onUpdateScope: this}

      for (let i = 0; i < oldValue.length; i++) {
        // Turn the current index into a string
        let key = i.toString()
        tweenedData[key] = oldValue[i]
        tweenSourceData[key] = newValue[i]
      }

      // Tween over the our target dummy object, but only for the specific key
      TweenMax.to(tweenedData, 1, tweenSourceData)
    }
  }
});