CODEWITHSUNDEEP
javascript
Kyle Tech
Kyle Tech

Reputation: 61

Compare between two arrays

While I was thinking in someway to compare between two arrays, accidentally for the first time something like this happens with me.. something worked with me for the first time without showing me any errors!

This is a very simplified visualization for an application I'm working on currently. I have two arrays, one called options, the other is called correct. so the options are options of some question, the chances are the chances of this question. in this example two of the options are correct answers.. so what I have to do is to compare between this two arrays to check if it returns true (later) or if it's returning false (not included in the code).

could you please explain for me how this actually worked?

const options = ['facebook', 'twitter', 'tango', 'skype'];
const correct = ['twitter', 'skype'];

const trueIndexes = [];
options.forEach((cur, index) => {
  correct.forEach((cur1, index1) => {
    if (cur === cur1) {
      trueIndexes.push(index);
    }
  });
});
console.log(trueIndexes);

Upvotes: 0

Views: 65

Answers (3)

Rainer Plumer
Rainer Plumer

Reputation: 3753

As explained by others, you just iterate over all the combinations of these 2 arrays and collect the indexes where an option is in both arrays(in other words, if an option is true)

I just wanted to add that you should perhaps change your data structure so that options are stored with the questions...and correct answers are indicated by a flag so they don't need to be looked up.

For example:

const questions = [
        {
            id: 'social_1',
            question: 'Which of these are popular social media sites?',
            answers: [
                {id: 'fb', label: 'Facebook', correct: true},
                {id: 'skype', label: 'Skype', correct: false},
                {id: 'twitter', label: 'Twitter', correct: true},
                {id: 'yt', label: 'YouTube', correct: false},
            ]

        }, {
            id: 'cars_1',
            question: 'Which of these are car brands?',
            answers: [
                {id: 'tesla', label: 'Tesla', correct: true},
                {id: 'bmw', label: 'BMW', correct: true},
                {id: 'twitter', label: 'Twitter', correct: false},
                {id: 'yt', label: 'YouTube', correct: false},
            ]

        }
    ];

https://jsfiddle.net/rainerpl/L438qjms/26/

Upvotes: 1

Miaplacidus
Miaplacidus

Reputation: 545

There are nested forEach loops for each array, and during each inner loop there is a conditional test to ascertain if one element exists in the other. If so, the index of where the matching item exists in the other array is pushed to the new trueIndexes array.

Another way to write this is: 

const options = ['facebook', 'twitter', 'tango', 'skype']
const correct = ['twitter', 'skype']
const trueIndices = correct.reduce((_trueIndices, correctItem) => {
  let correctItemIndex = options.indexOf(correctItem)
  if(correctItemIndex  !== -1) _trueIndices.push(correctItemIndex)
  return _trueIndices
}, [])
console.log(trueIndices)

or

const options = ['facebook', 'twitter', 'tango', 'skype']
const correct = ['twitter', 'skype']
const trueIndices = []
correct.forEach((correctItem) => {
  let correctItemIndex = options.indexOf(correctItem)
  if(correctItem !== -1) trueIndices.push(correctItem)
})
console.log(trueIndices)

Both of these alternate solutions should be faster.

Benchmark performance test of the 3 different methods

Upvotes: 2

Wiingreen
Wiingreen

Reputation: 308

Your code goes through each option and compares it to both correct values. If they match the index of the option is added to the true indexes list.

So the comparisons are like follows:

  1. 'facebook' = 'twitter'? no
  2. 'facebook' = 'skype'? no
  3. 'twitter' = 'twitter'? YES -> add index to list
  4. 'twitter' = 'skype'? no
  5. 'tango' = 'twitter'? no
  6. 'tango' = 'skype'? no
  7. 'skype' = 'twitter'? no
  8. 'skype' = 'skype'? YES -> add index to list

Upvotes: 2

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