Iterating Through An Object In JavaScript

Question

If I have an object, like so:

const test = [
  { x: 'A', y:'1' },
  { x: 'A', y:'2' },
  { x: 'B', y:'1' },
  { x: 'A', y:'3' },
  { x: 'C', y:'1' },
];

How can I go through it, and find the in order sequence [A, B, C] from x, where [A, B, C] belongs to a unique y?

So far I tried iterating through the object using a for loop, finding all 'A', 'B', 'C', in order, but I cannot ensure that they all belong to the same y item.

Remember add = after const test

xsami
– xsami

2018-05-02 00:30:24 +00:00
Commented May 2, 2018 at 0:30 — xsami
– xsami, Commented May 2, 2018 at 0:30

CertainPerformance · Accepted Answer · 2018-05-02 00:32:16Z

3

Transform the array into an object of arrays corresponding to only one particular y first:

const test = [
  { x: 'A', y:'1' },
  { x: 'A', y:'2' },
  { x: 'B', y:'1' },
  { x: 'A', y:'3' },
  { x: 'C', y:'1' },
];
const reducedToYs = test.reduce((accum, { x, y }) => {
  accum[y] = (accum[y] || '') + x;
  return accum;
}, {});
const found = Object.entries(reducedToYs)
  .find(([y, str]) => str.includes('ABC'));
console.log('y: ' + found[0] + ', entire string: ' + found[1]);

answered May 2, 2018 at 0:32

CertainPerformance

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2 Comments

BlueishVelvet Over a year ago

Thank you, this is great. I should learn how to use these properly. Just curious, was this something that was possible with a for loop? Thank you.

CertainPerformance Over a year ago

Sure, you can do anything with a for loop - which is exactly the problem with for loops IMO. Using the array methods instead offers better abstraction, does not require manual iteration, and gives a clearer picture of what the function is doing.

gavgrif · Accepted Answer · 2018-05-02 01:21:14Z

0

Create a function that takes the target Y value. Loop through the test array and compare the y value to your target value and if it matches - push the x value into an array. Then return that array.

If a string is required ("ABC)" then rather than creating an array create a string and append the x value to it to build the string that is then returned.

const test = [
  { x: 'A', y:'1' },
  { x: 'A', y:'2' },
  { x: 'B', y:'1' },
  { x: 'A', y:'3' },
  { x: 'C', y:'1' },
];



function testValue(str) {
    let xArray = [];
    test.forEach(function(item) { 
      if(item['y'] === str) {xArray.push(item['x'])}
   })
  return xArray;
  }
  
console.log(testValue('1')) // gives ["A", "B", "C"]

edited May 2, 2018 at 1:21

answered May 2, 2018 at 1:05

gavgrif

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