派生索引数组

Question

This is a continuation of exploration traversing data structures in JavaScript. See here and here .

Given this Javascript object:

var parsed =       {
  "terms": [
    {
      "span": [
        12,
        13
      ],
      "value": "2",
      "label": "number"
    },
    {
      "span": [
        13,
        14
      ],
      "value": "x",
      "label": "multiply"
    },
    {
      "span": [
        14,
        16
      ],
      "value": "14",
      "label": "number"
    },
  ],
  "span": [
    12,
    21
  ],
  "weight": 0.85,
  "value": "2x14 test"
};

How would I derive an array of the indexes of the terms where the label: number?

In a previous question, noted above, I was able to solve the notion of deriving the index for a certain label, when it was known that there was only one instance of such.

parsed.terms.map(function(d){ return d['label']; }).indexOf('number');

Now I am faced with the notion of multiple instances, as in the object above. The above code snip will only derive the index of the first.

I could build an array by looping through the terms and see if each has a number label, however the ideal solution would perhaps expand or modify the code snip above and perhaps not use a loop.

Answer 1

When you need to map and filter simultaneously use reduce :

var indexes = parsed.terms.reduce(function(indexCollection, item, index) {
    if(item.label === 'number') {
        indexCollection.push(index);
    }

    return indexCollection;
}, []);