How to optimize array lookup of JS object based on one property

Question

We have a large array of objects:

var englishStudents = [
    {StudentId: 1, Name: "John"},
    {StudentId: 2, Name: "Jack"},
    {StudentId: 3, Name: "Jane"}
];

Need to check if another similar object is contained in this array, just by comparing one property alone.

var randomStudent = {StudentId: 1337, Name: "Foo"};

This is what I have, and it seems as though it will work, but I don't think this is the best way to do this.

var studentIds = $.map(englishStudents, function (student, index) { return student.StudentId; });
var randomStudentLearnsEnglish = false;
for (var sId in studentIds) {
    if (randomStudent.StudentId == sId) {
        randomStudentLearnsEnglish = true;
        break;
    }
}

What would be the optimized way to do this?

That seems efficient enough. Are you having performance issues? — elclanrs
– elclanrs, Commented Jan 31, 2013 at 22:26
Is the array sorted? Is there a reason they're in an array, and not in something keyed by the ID? — Dave Newton
– Dave Newton, Commented Jan 31, 2013 at 22:27
@elclanrs: I was looking to make the two loops in there to one, somehow. — Hari Pachuveetil
– Hari Pachuveetil, Commented Jan 31, 2013 at 22:40
@FloydPink Then unless you have some form of backing index, iteration is the only option. — Dave Newton
– Dave Newton, Commented Jan 31, 2013 at 22:47

npclaudiu · Accepted Answer · 2013-01-31 22:31:22Z

2

You should keep student data in a hash table like JHashtable instead of the array. For mor complex scenarios, you can maintain more than one hash table, like studentsById, studentsByCountryCode, etc.

answered Jan 31, 2013 at 22:31

npclaudiu

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Comments

charlietfl · Accepted Answer · 2013-01-31 22:39:25Z

1

If all you want to know is if the ID exists can do this:

function checkIdExists( id){
    /* map array of matching ID, if none exists length of array is zero*/
    return  $.map(englishStudents, function (student, index) { 
               return student.StudentId==id; 
    }).get().length;
});

Use:

 if( checkIdExists( 1234)){
     /* run exists code*/
 }

answered Jan 31, 2013 at 22:39

charlietfl

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1 Comment

Hari Pachuveetil Over a year ago

Thanks. This is exactly what I want. Although after looking at this answer (stackoverflow.com/a/9283885/218882), I feel $.grep() would be faster, but maybe they're the same.

dchhetri · Accepted Answer · 2013-01-31 22:30:49Z

1

If you really want, you can create a further indexing scheme:

var englishStudents = [
    {StudentId: 1, Name: "John"},
    {StudentId: 2, Name: "Jack"},
    {StudentId: 3, Name: "Jane"}
];
 //if doing this a lot of time, take the one time hit of construction and memory
var idToNameMap = createIdToNameMap(englishStudents); //returns {'1': 'John', '2': Jack' , '3': 'Jane'}

var randomStudent = getRandomStudent();
if( idToNameMap[ randomStudent.StudentId] != undefined){ ... }

answered Jan 31, 2013 at 22:30

dchhetri

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Comments

doogle · Accepted Answer · 2013-01-31 22:36:48Z

1

Just do a hash instead of an array, so:

var englishStudents = {
    1: {StudentId: 1, Name: "John"},
    2: {StudentId: 2, Name: "Jack"},
    3: {StudentId: 3, Name: "Jane"}
};

and then to retrieve, simply do:

var student = englishStudents[id];

edited Jan 31, 2013 at 22:36

answered Jan 31, 2013 at 22:30

doogle

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1 Comment

charlietfl Over a year ago

your object syntax is invalid

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