Filter nested array of objects by object property in d3.js

Question

I have a meteorite landings dataset.
I nested the data in four keys, by type:

  var dataByType = d3.nest()
    .key(function(d) {
          return d.rectype;
    })
    .entries(dataset); // the original array

This is the resulting structure: data

Now I want to create new arrays , filtering the nested one: I want each filtered array to contain only the objects whose "mass" property is inside a defined range .
So I tried this:

// filter small meteorites
var lightWeight = dataByType.forEach(function(d){
      d.values.filter(function (object) {
            var mass = object.mass;
            return mass <= 100;
      });
  });

But it returns undefined .

Nesting is giving me a lot of trouble! What do I do wrong?
Thanks in advance

Answer 1

I think you're overwriting lightWeight on each pass of that forEach. Instead try creating lightWeight as its own object, then adding the keys you want in the loop:

const lightWeight = {};

dataByType.forEach(function(d){
  lightWeight[d.key] = d.values.filter(function (object) {
    var mass = object.mass;
    return mass <= 100;
  });
});

Working pen which (I think?) is doing what you want: https://codepen.io/benjaminwfox/pen/veBjrP?editors=0012

Answer 2

我无法说出你的数据集是什么样的，但是它可能只是你最后没有返回lightWeight吗？

Answer 3

I am unsure what you are trying to filter on exactly, but try to use map instead of forEach and you need to return d in the iterators, anon function.

Like the following:

var lightWeight = dataByType.map(function(d) {
    d.filteredValues = d.values.filter(function (object) {
        return object.mass <= 100;
    });
    return d;
});

Answer 4

Assuming that you got the data in the format you shared, where for each item of data you have a key property and a values array.

If you want to filter the values array by the mass property of each entry, you will need to use a combination of .map() and .filter() methods.

This is how should be your code:

var lightWeight = data.map(function(d){
    var obj = {};
    obj.key = d.key;
    obj.values = d.values.filter(function (object) {
            return object.mass <= 100;
    });
    return obj;
});

This will give you the expected results.