Transform an array of IDs into an array of strings using a list of objects

Question

Transform an array of IDs into an array of strings using a list of objects

var myIds = [3, 4, 2];

var myObj = [
    {id:1, name:'one'}, 
    {id:2, name:'two'},
    {id:3, name:'tree'},
    {id:4, name:'four'}];

// need to obtain ['tree', 'four', 'two']

var idsToNames= function(ids, objects) {
    var myNames = myIds.map(function(id){
        // transform id to name
        foreach(o in objects){
            if (i.id == id) 
                return o.name;
        }
    });
    return myNames;
}

Is this the most efficient method for converting an array of ids into an array of corresponding names?

javascript arrays object

Answer 1

Answer №1

To start, modify your object in the following way

var newMyObj = myObj.reduce(function(result, currentObject) {
  result[currentObject.id] = currentObject.name;
  return result;
}, {});

console.log(newMyObj);
// { '1': 'one', '2': 'two', '3': 'three', '4': 'four' }

You can alternatively create newMyObj by looping through the array myObj, like this as well

var newMyObj = {};
for (var i = 0; i < myObj.length; i += 1) {
  newMyObj[myObj[i].id] = myObj[i].name;
}

Now, you can easily iterate over myIds and retrieve values from newMyObj, like this

console.log(myIds.map(function(id) { return newMyObj[id]; }));
// [ 'three', 'four', 'two' ]

If your environment supports ECMAScript 2015's Arrow functions, this can be expressed concisely as

console.log(myIds.map((id) => newMyObj[id]));
// [ 'three', 'four', 'two' ]

By converting your original myObj to newMyObj you will achieve constant time lookup. Otherwise, you would need to loop through the myObj array for every element in the myIds, making the runtime complexity O(n*m).

Answer 2

To start, modify your object in the following way

var newMyObj = myObj.reduce(function(result, currentObject) {
  result[currentObject.id] = currentObject.name;
  return result;
}, {});

console.log(newMyObj);
// { '1': 'one', '2': 'two', '3': 'three', '4': 'four' }

You can alternatively create newMyObj by looping through the array myObj, like this as well

var newMyObj = {};
for (var i = 0; i < myObj.length; i += 1) {
  newMyObj[myObj[i].id] = myObj[i].name;
}

Now, you can easily iterate over myIds and retrieve values from newMyObj, like this

console.log(myIds.map(function(id) { return newMyObj[id]; }));
// [ 'three', 'four', 'two' ]

If your environment supports ECMAScript 2015's Arrow functions, this can be expressed concisely as

console.log(myIds.map((id) => newMyObj[id]));
// [ 'three', 'four', 'two' ]

By converting your original myObj to newMyObj you will achieve constant time lookup. Otherwise, you would need to loop through the myObj array for every element in the myIds, making the runtime complexity O(n*m).

Transform an array of IDs into an array of strings using a list of objects

Answer №1

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