jquery.inArray() function not working

Question

I am having a array as follows

       var nameIDHashMap = [];
       nameIDHashMap.push({
            key: name,
            value: xmlLength
       });
     startToEnd.push({
          key: $(this).attr("startFrom"),
          value: $(this).attr("endTo")
    });

I m trying to use the inArray() function like shown below

            var variablestart = startToEnd[0].key;
            alert("The variable Start is :"+variablestart);
            var toEnd;
            if(jQuery.inArray(variablestart,nameIDHashMap) > -1) {
                alert('found');
            }
            if ($.inArray(variablestart, nameIDHashMap) != -1) 
            {
                alert("Found");
            //  toEnd = startToEnd[connectWindow].value
            }
            else
                alert("Fail");

I dont know why always the else loop is called. None of the if loop is getting called. Both of the array has that same key present. Please let me know where I am doing wrong.Thanks!

variablestart is a property of an element in the array, not an element in the array. — jbabey
– jbabey, Commented Sep 6, 2012 at 18:17
@jbabey: I didnt get you. What do you mean by property of an element. I think it is just the variable having some value. Is there any thing else then I can do this — unix_user
– unix_user, Commented Sep 6, 2012 at 18:19
because in your example variablestart equals lets say 'some name', but element of your array looks like {key: 'some name', value: 10} — Alexander Larikov
– Alexander Larikov, Commented Sep 6, 2012 at 18:21

jbabey · Accepted Answer · 2012-09-06 18:20:47Z

3

variablestart is a property of an element in the array, not an element in the array.

var nameIDHashMap = [];
nameIDHashMap.push({
    key: 'foo',
    value: 'bar'
});

$.inArray(nameIDHashMap[0].key, nameIDHashMap); // this is not an element, -1
$.inArray(nameIDHashMap[0], nameIDHashMap); // this is an element, 0

You are essentially trying to equate the object { key: 'foo', value: 'bar' } to the string 'foo', which are not equal.

http://jsfiddle.net/jbabey/kgYSe/

answered Sep 6, 2012 at 18:20

jbabey

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3 Comments

unix_user Over a year ago

Ok. Is there a way to do a look up based on the key. I need to get the key from one key value array and then look for the value from another key value array.

jbabey Over a year ago

@unix_user see pointy's answer. using an object literal instead of an array will allow you to do that.

unix_user Over a year ago

Can you please help me with this jsfiddle jsfiddle.net/unix_user/kgYSe/3 . I need to find and see if the key is present in both the hash table. How would i do this?

Pointy · Accepted Answer · 2012-09-06 18:50:50Z

1

That's not how .inArray() works. It searches for an array element that's equal to the value you pass in. It doesn't have any provisions for a comparison function.

Even if it did work, what you're assembling there isn't a "hash table". If you want to do efficient lookups by key, you can just create named properties on a simple object:

var map = {};
map.someKey = someValue;

The .inArray() method and anything like it performs a linear-time search through the array, and that's not a very efficient way to do things if you're going to have an "interesting" number of key/value pairs.

edit — if you really must keep a linear unindexed list of named properties, you could use a lookup function like this:

function find( list, key, test ) {
  test = test || function(e) { return e ? e.key == key : false; };

  for (var i = 0; i < list.length; ++i)
    if (test(list[i])) return i;
  return -1;
}

To use that, you'd just do:

if (find(nameIDHashMap, someKey) >= 0) {
  alert("Found!");
}

edited Sep 6, 2012 at 18:50

answered Sep 6, 2012 at 18:19

Pointy

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6 Comments

jbabey Over a year ago

+1 for suggesting to use an object instead of an array of objects

unix_user Over a year ago

@Pointy:: Can you please help me with this jsfiddle jsfiddle.net/unix_user/kgYSe/3 . I need to find and see if the key is present in both the hash table. How would i do this?

Pointy Over a year ago

@unix_user the point I and jbabey are trying to make is that you can't use $.inArray() to do what you're trying to do. You can write your own function, however, but in general it'd be much more efficient to use an object to store properties on. I'll update my answer.

unix_user Over a year ago

@Pointy: Thanks for the update. I am still confused that at what time the inArray is used? As well, I got confused now on when and for what purpose it should be used.

Pointy Over a year ago

@unix_user well $.inArray() is useful when you have a simple array of strings or numbers. With objects, it's complicated because there's no JavaScript concept of Object equality besides "are these two things exactly the same object?" - not the same properties and values, but exactly the same object stored in memory. Sometimes that's what you want, but not in a case like yours.

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