title: Error in showing min() and max() result in D3
body: <p>I not sure why d3.min() and d3.max() return the same result in the end. Here is the code:</p>
  
  <pre><code>var groupByAgeAndtime = d3.nest()
                .key(function(d) { return d.age; })
                //.key(function(d) { return d.time_in_hospital; })
                .rollup(function(v) {
                  return{
                      mean_time_in_hospital : d3.mean(v, function(d){ return d.time_in_hospital;})
                } })
                .object(datapoints);
  
      console.log(groupByAgeAndtime);
  
      var radiusScale = d3.scaleSqrt().domain([d3.min(Object.keys(groupByAgeAndtime), function(d){
                            return groupByAgeAndtime[d];//minimum average time spent
                          }),d3.max(Object.keys(groupByAgeAndtime), function(d){
                            return groupByAgeAndtime[d];//maximum average time spent
                          })]).range([50,150])
  
      console.log('Min: ',d3.min(Object.keys(groupByAgeAndtime), function(d){
                            return groupByAgeAndtime[d];//manimum average time spent
                          }));
  
      console.log('Max: ',d3.max(Object.keys(groupByAgeAndtime), function(d){
                            return groupByAgeAndtime[d];//maximum average time spent
                          }));
  </code></pre>
  
  <p>Here is the screenshot of the console in Mozilla Firefox:
  <a href="https://i.stack.imgur.com/Xnmfm.png" rel="nofollow noreferrer">Screenshot</a></p>
  
  <p>Hhere is the link for my jsfiddle: <a href="https://jsfiddle.net/james_bond100/c8rgfb9k/" rel="nofollow noreferrer">Link</a></p>
  
  <p>Can anyone explain to me why it behave like that? Where did I do wrong in the code?</p>