d3.js - Runtime of d3.nest()

Question

I was wondering how d3.nest() works and what runtime it has. E.g.

newData = d3.nest()
      .key(function(d){
        return d.age
      })
      .entries(data)
      .map(function(group){
        return {
          node : group.key
        }
      })

Is it O(n), also with map? And what happens with a level 2 nest?

newData = d3.nest()
          .key(function(d){
            return d.age
          })
          .key(function(d){
            return d.year
          })
          .entries(data)

Answer 1

等待大神答复