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I want to reduce an array of objects like this:

var data = [{
    item: "Item 1",
    pages: 30,
    chapters: 3
    },
    {
    item: "Item 1",
    pages: 50,
    chapters: 3
    },
    {
    item: "Item 2",
    pages: 10,
    chapters: 3
    }
    ]

But aggregating two "fields", so in this case it should end like this:

  [
    {item: "Item 1", pages: 80, chapters: 6},
    {item: "Item 2", pages: 10, chapters: 3}
  ]

I’ve tried with a reduce but I can’t aggregate more than one field:

data.reduce((acc,cur) => {
    acc[cur.item][pages] = acc[cur.item][pages] + cur.item.pages || cur.item.pages
    acc[cur.item][chapters] = acc[cur.item][chapters] + cur.item.chapters || cur.item.chapters
    return acc
},{})

But this throws errors since it doesn’t find the pages item in the accumulator.

Is it possible to reduce aggregating more than one field of data?

2

Answers


  1. var data = [{
        item: "Item 1",
        pages: 30,
        chapters: 3
    },
    {
        item: "Item 1",
        pages: 50,
        chapters: 3
    },
    {
        item: "Item 2",
        pages: 10,
        chapters: 3
    }];
    
    const processedData = data.reduce((items, { item, pages, chapters }) => {
        const ensureItemData = () =>
            items.find(itemData => itemData.item === item)
            ?? (() => {
                const itemData = { item, pages: 0, chapters: 0 };
                items.push(itemData);
                return itemData;
            })();
    
        const itemData = ensureItemData();
        itemData.pages += pages;
        itemData.chapters += chapters;
    
        return items;
    }, []);
    
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  2. You can achieve this by using reduce and properly initializing the accumulator:

    const data = [
      { item: "Item 1", pages: 30, chapters: 3 },
      { item: "Item 1", pages: 50, chapters: 3 },
      { item: "Item 2", pages: 10, chapters: 3 }
    ];
    
    let result = data.reduce((acc, cur) => {
      if (!acc[cur.item]) {
        acc[cur.item] = { item: cur.item, pages: 0, chapters: 0 };
      }
      acc[cur.item].pages += cur.pages;
      acc[cur.item].chapters += cur.chapters;
      return acc;
    }, {});
    
    result = Object.values(result);
    console.log(result);
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