从对象数组中提取 object 元素并将它们组织成数组

Question

After days of hairpulling, I decided to seek help:

• I have an array of objects, one for each grocery store item. Each object has 3 properties: category (string for category of item), itemName (string for item itself), and onSale (boolean whether it's on sale or not):

   var itemData = [ { category: 'fruit', itemName: 'apple', onSale: false }, { category: 'canned', itemName: 'beans', onSale: false }, { category: 'canned', itemName: 'corn', onSale: true }, { category: 'frozen', itemName: 'pizza', onSale: false }, { category: 'fruit', itemName: 'melon', onSale: true }, { category: 'canned', itemName: 'soup', onSale: false }, ];

• I need to convert it into an object whose properties are the object categories. Each property is an array containing values in itemName that correspond to the property:

   { fruit: ['apple', 'melon($)'], canned: ['beans', 'corn($)', 'soup'], frozen: ['pizza'] };

• When I try to do it, I end up with directionally correct values, except they're repeated:

   { fruit: [ 'apple', 'apple', 'melon', 'melon', 'melon' ], canned: [ 'beans', 'beans', 'corn', 'corn', 'corn', 'soup', 'soup', 'soup' ], frozen: [ 'pizza', 'pizza' ] }

• I spent hours trying to find out where I went wrong, to no avail. Here's my code:

   function organizeItems (array){ //create output obj var output = {} //iterate over the array for(var i = 0; i < array.length; i++){ //iterate over the object in the array for(var category in array[i]){ //if value of category isn't in output add the value to output as an empty array if(output[array[i]["category"]] === undefined){ output[array[i]["category"]] = []; //if not --> push the itemName to the category } else{ output[array[i]["category"]].push(array[i]["itemName"]) } } } return output }

How can I avoid the repetition and end up with the correct values in the arrays?

Answer 1

for(var category in array[i]){...

You don't have to iterate through the entries of each object as that will add unnecessary elements to the array like in your output 'melon', 'melon', 'melon'

---

You can use Array.prototype.reduce :

 const itemData = [ { category: 'fruit', itemName: 'apple', onSale: false }, { category: 'canned', itemName: 'beans', onSale: false }, { category: 'canned', itemName: 'corn', onSale: true }, { category: 'frozen', itemName: 'pizza', onSale: false }, { category: 'fruit', itemName: 'melon', onSale: true }, { category: 'canned', itemName: 'soup', onSale: false }, ]; const object = itemData.reduce((acc,el) => (acc[el.category]??= [], acc[el.category].push(el.itemName + (el.onSale? '($)': '')), acc), {}) console.log(object)

Answer 2

You could group by category and adjust itemName .

 const itemData = [{ category: 'fruit', itemName: 'apple', onSale: false }, { category: 'canned', itemName: 'beans', onSale: false }, { category: 'canned', itemName: 'corn', onSale: true }, { category: 'frozen', itemName: 'pizza', onSale: false }, { category: 'fruit', itemName: 'melon', onSale: true }, { category: 'canned', itemName: 'soup', onSale: false }], result = itemData.reduce((r, { category, itemName, onSale }) => { itemName += onSale? ' ($)': ''; (r[category]??= []).push(itemName); return r; }, {}); console.log(result);

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Answer 3

 var itemData = [ { category: 'fruit', itemName: 'apple', onSale: false }, { category: 'canned', itemName: 'beans', onSale: false }, { category: 'canned', itemName: 'corn', onSale: true }, { category: 'frozen', itemName: 'pizza', onSale: false }, { category: 'fruit', itemName: 'melon', onSale: true }, { category: 'canned', itemName: 'soup', onSale: false }, ]; // // expected result... // { // fruit: ['apple', 'melon($)'], // canned: ['beans', 'corn($)', 'soup'], // frozen: ['pizza'] // }; console.log( itemData.reduce((result, item) => { // destructure `itemData`'s array `item`. const { category, itemName, onSale } = item; // (create and/or) access the `category` specific array. const categoryArray = (result[category]??= []); // push the correct (depending on `onSale` state) form of a category item. categoryArray.push(`${ itemName }${ (onSale === true)? '($)': '' }`); return result; }, {}) );

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