如何基于一个属性优化JS对象的数组查找

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?

Answer 1

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.

Answer 2

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];

Answer 3

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){ ... }

Answer 4

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*/
 }