在crossfilter.js中按多个维度排序

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问题描述

我正在使用Mike Bostock的库来过滤和排序大型数据集。我的问题：鉴于具有多个维度的数据集，我如何一次对多个维度进行排序？

I'm using Mike Bostock's crossfilter library to filter and sort large datasets. My problem: Given a dataset with multiple dimensions, how can I sort on more than one dimension at a time?

测试数据集：

[
    { cat: "A", val:1 },
    { cat: "B", val:2 },
    { cat: "A", val:11 },
    { cat: "B", val:5 },
    { cat: "A", val:3 },
    { cat: "B", val:2 },
    { cat: "A", val:11 },
    { cat: "B", val:100 }
]

所需输出的示例，按 cat，val （升序）：

Example of desired output, sorting by cat, val (ascending):

[
    { cat: "A", val:1 },
    { cat: "A", val:3 },
    { cat: "A", val:11 },
    { cat: "A", val:11 },
    { cat: "B", val:2 },
    { cat: "B", val:2 },
    { cat: "B", val:5 },
    { cat: "B", val:100 }
]

到目前为止我使用的方法对我们来说所需维度的字符串连接：

The approach I've used thus far is to use string concatenation on the desired dimensions:

var combos = cf.dimension(function(d) { return d.cat + '|' + d.val; });

这适用于多个基于字符串的维度，但不适用于数字维度，因为它是不是一种自然的排序（'4'> '11'）。我想我可以在数字上使用零填充来完成这项工作，但是对于大型数据集来说这可能会变得昂贵，所以我宁愿避免使用它。有没有其他方法可以在这里工作，使用crossfilter？

This works fine with multiple string-based dimensions, but won't work with numeric dimensions, as it's not a natural sort ('4' > '11' ). I think I could make this work with zero-padding on the numbers, but this could get expensive for a large dataset, so I'd prefer to avoid it. Is there another way that might work here, using crossfilter?

任何允许不同维度具有不同排序方向的解决方案的加分点（升序/降序）。

Bonus points for any solution that allows different dimensions to have different sort directions (ascending/descending).

澄清：是的，我可能需要切换到原生 Array.sort 实施。但是使用crossfilter的重点在于它非常非常快，特别是对于大型数据集，它以一种使重复排序更快的方式缓存排序顺序。所以我真的在这里寻找一个基于crossfilter的答案。

Clarification: Yes, I may need to switch to a native Array.sort implementation. But the whole point of using crossfilter is that it's very, very fast, especially for large datasets, and it caches sort order in a way that makes repeated sorts even faster. So I'm really looking for a crossfilter-based answer here.

`推荐答案`

这就是我最终做的事情：

Here's what I ended up doing:

 
 我仍然在单个新维度上使用字符串连接，但是
 
  我将度量转换为使用crossfilter获取最小值/最大值之前的正数，可比较的十进制数：

I still use string concatenation on a single new dimension, but
I convert the measure to a positive, comparable decimal before turning it into a string, using crossfilter to get the min/max:

var vals = cf.dimension(function(d) { return d.val }),
    min = vals.bottom(1)[0].val,
    offset =  min < 0 ? Math.abs(min) : 0,
    max = vals.top(1)[0].val + offset,
    valAccessor = function(d) {
        // offset ensures positive numbers, fraction ensures sort order
        return ((d.val + offset) / max).toFixed(8);
    },
    combos = cf.dimension(function(d) { 
        return d.cat + '|' + valAccessor(d); 
    });

查看工作小提琴：

这样做的好处是可以正确处理负数 - 据我所知，零填充是不可能的。它似乎同样快。缺点是它需要在数字列上创建一个新维度，但在我的情况下，我通常要求在任何情况下。

This has the advantage of handling negative numbers properly - not possible with zero-padding, as far as I can tell. It seems to be just as fast. The downside is that it requires creating a new dimension on the numeric column, but in my case I usually require that in any case.

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Crossfilter