javascript - 重命名 d3.nest() 中的键和值

Question

Learn JS Data给出了 split-apply-combine with

的例子

var expenseMetrics = d3.nest()
  .key(function(d) { return d.name; })
  .rollup(function(v) { return {
    count: v.length,
    total: d3.sum(v, function(d) { return d.amount; }),
    avg: d3.mean(v, function(d) { return d.amount; })
  }; })
  .entries(expenses);
console.log(JSON.stringify(expenseMetrics));

结果是

[{"key":"jim","values":{"count":2,"total":79,"avg":39.5}},
 {"key":"carl","values":{"count":1,"total":120.11,"avg":120.11}},
 {"key":"stacy","values":{"count":3,"total":90.9,"avg":30.3}}]

是否有任何简单的方法来转换 nest 的输出，以便 key 具有自定义名称并且 values 被展平，从而产生如下输出

[{"name":"jim","count":2,"total":79,"avg":39.5},
 {"name":"carl","count":1,"total":120.11,"avg":120.11},
 {"name":"stacy","count":3,"total":90.9,"avg":30.3}]

This question似乎相关，但提供的 fiddle 中的解决方案很难概括。

Answer 1

没有办法让 d3.nest() 做到这一点(至少在版本 3 中没有；它有可能在 v4 中添加，但我对此表示怀疑)。

但你当然可以这样做:

var expenseMetrics = d3.nest()
  ...
  .entries(expenses)
  .map(function(group) {
    return {
      name: group.key,
      count: group.values.count,
      total: group.values.total,
      avg:   group.values.avg
    }
  });

如果你想让它更通用，你可以获得与上面相同的输出而无需硬编码任何东西(除了 key => name 映射，它无论如何都适合硬编码):

var expenseMetrics = d3.nest()
  ...
  .entries(expenses)
  .map(function(group) {
    var merged = { name: group.key };

    // Copy each key-val pair of group.values into merged
    Object.keys(group.values).forEach(function(key) {
      merged[key] = group.values[key];
    });

    return merged;
  });