Javascript: How to combine two arrays with duplicate keys into an object-CodePudding

I have two arrays

array1 = [Alabama, Alabama, Georgia, Georgia, Georgia, California ]
array2 = [Mobile, Montgomery, Atlanta, Savannah, Montgomery, San Francisco ]

Both have equal number of elements and essentially for every city in Array 2, there is a corresponding state in the other array but as you can see city names in different states can be the same

I need to convert it into an Object like this in Javascript - This way I can populate a conditional drop down easily when a state is chosen unless someone has an idea to do the same with 2 distinct arrays

var citiesByState = {
   Alabama: ["Mobile","Montgomery"],
   Georgia: ["Savannah","Montgomery"],
   California: ["San Francisco"]
}

Any help would be greatly appreciated

I have tried a few different ways but they create objects of objects as opposed to what I want above.

CodePudding user response：

The Solution :

Don't forget to give a feedback.

const array1 = ['Alabama', 'Alabama', 'Georgia', 'Georgia', 'Georgia', 'California' ];

const array2 = ['Mobile', 'Montgomery', 'Atlanta', 'Savannah', 'Montgomery', 'San Francisco'];

const objProps = Array.from(new Set(array1));
const citiesByState = {};

objProps.forEach(state => {
  citiesByState[state] = [];
})

array1.forEach((state, idx) => {
  citiesByState[state].push(array2[idx]);
})

console.log(citiesByState);

CodePudding user response：

I believe the following code solves your question.

let array1 = ["Alabama", "Alabama", "Georgia", "Georgia", "Georgia", "California"];
let array2 = ["Mobile", "Montgomery", "Atlanta", "Savannah", "Montgomery", "San Francisco"];

let citiesByState = {};
for (let [index, state] of array1.entries()) {
  if (!citiesByState[state]) {
    // if the state has not been added yet, add it
    citiesByState[state] = [];
  }
  // push the corresponding city index onto the state array
  citiesByState[state].push(array2[index]);
}

console.log(citiesByState);

CodePudding user response：

Here is an example with reduce:

let array1 = ['Alabama', 'Alabama', 'Georgia', 'Georgia', 'Georgia', 'California' ]
let array2 = ['Mobile', 'Montgomery', 'Atlanta', 'Savannah', 'Montgomery', 'San Francisco' ]
let result = array1.reduce((memo, state, idx) => {
  if(!memo[state]){
     memo[state] = array2[idx];
  } else {
    const rest =  Array.isArray(memo[state]) ? memo[state].flat() : [memo[state]]
    memo[state] = [array2[idx], ...rest];
  }
  return memo;  
}, {});

console.log(result)

CodePudding user response：

Clean and fewer lines

var array1 = ["Alabama", "Alabama", "Georgia", "Georgia", "Georgia", "California", "Alabama"];

var array2 = ["Mobile", "Montgomery", "Atlanta", "Savannah", "Montgomery", "San Francisco", "test"];

const res = array1.reduce((ac,a, index) => {
  let key = a;
  ac[key] = ac[key] || [];
  ac[key].push(array2[index])
  return ac;
}, {});

console.log(res)