If value is in a list

**Tom Cole** · Jun 27 '08, 07:09 PM

Re: If value is in a list

On Apr 22, 2:43 pm, Mike <mpea...@gmail. comwrote:

I have a list of numbers, e.g., (1,3,4,5,8,16,2 0), and am trying to
create a simple IF statement to see if the value is in that list. Is
there an easier or more efficient way, than the sample code below, to
do it?
>
=====
>
<script type="text/javascript">
num = 2;
list = [1,3,4,5,8,16,20];
if(isInList( num, list )) {
alert("It's there!");} else {
>
alert("It's NOT there!");
>
}
>
function isInList( num, list ) {
// List is an Array()
result = false;
for(i in list) {
if(num == list[i]) { result = true }
}
return result}
>
</script>

What about alert(num in list);

**Mike** · Jun 27 '08, 07:09 PM

Re: If value is in a list

What about alert(num in list);- Hide quoted text -

Yes, that would work, but I'm actually concerned about the isInList
function. I imagine there's some way to avoid the whole for(i in
list) routine. For example, is there a way to do this:

function isInList( number, list ) {
if(number == anyElementIn( list ) { return true } else { return
false }
}

is there some built in javascript method that will check a value
against any value in an Array?

Thanks!

Mike

**Tom Cole** · Jun 27 '08, 07:09 PM

Re: If value is in a list

On Apr 22, 3:12 pm, Mike <mpea...@gmail. comwrote:

What about alert(num in list);- Hide quoted text -

>
Yes, that would work, but I'm actually concerned about the isInList
function. I imagine there's some way to avoid the whole for(i in
list) routine. For example, is there a way to do this:
>
function isInList( number, list ) {
if(number == anyElementIn( list ) { return true } else { return
false }
>
}
>
is there some built in javascript method that will check a value
against any value in an Array?
>
Thanks!
>
Mike

I've looked around as I'm not aware of one. The best I can come up
with is:

function doCheck(value, array) {
for (var i = 0; i < array.length; i++) {
if (array[i] == value) {
return true;
}
}
return false;
}

This method returns immediately upon a success, rather than looping
through the entire array every time as your first example did.

**Peroli** · Jun 27 '08, 07:09 PM

Re: If value is in a list

On Apr 23, 12:12 am, Mike <mpea...@gmail. comwrote:

What about alert(num in list);- Hide quoted text -

>
Yes, that would work, but I'm actually concerned about the isInList
function. I imagine there's some way to avoid the whole for(i in
list) routine. For example, is there a way to do this:
>
function isInList( number, list ) {
if(number == anyElementIn( list ) { return true } else { return
false }
>
}
>
is there some built in javascript method that will check a value
against any value in an Array?
>
Thanks!
>
Mike

Mike,
You can use "indexOf" (Javascript 1.6, so won't work in IE) method
on an array instead. But its performance differs from browser to
browser.
"num in list" is faster in Firefox, but slower in Safari.

--- script ---

<html>
<head>
<title>Benchmar k</title>
</head>
<body>
<form id="test_form" >
<input type="button" value="Benchmar k" onclick="benchm ark()">
</form>
<span id="result" />
<script type="text/javascript">
function benchmark() {
var a = [1,3,4,5,8,16,20];
var d = new Date();
for(var i=0; i<100000; i++) {
var a1 = a.indexOf(8);
}
var t1 = (new Date()) - d;
d = new Date();
for(var i=0; i<100000; i++) {
var a1 = 8 in a;
}
var t2 = (new Date()) - d;
document.getEle mentById('resul t').innerHTML = "indexOf:" + t1 +
'<br />in:' + t2;
}
</script>
</body>
</html>

-- Peroli Sivaprakasam

**Paul Lautman** · Jun 27 '08, 07:09 PM

Re: If value is in a list

Mike wrote:

>What about alert(num in list);- Hide quoted text -

>
Yes, that would work, but I'm actually concerned about the isInList
function. I imagine there's some way to avoid the whole for(i in
list) routine. For example, is there a way to do this:
>
function isInList( number, list ) {
if(number == anyElementIn( list ) { return true } else { return
false }
}
>
is there some built in javascript method that will check a value
against any value in an Array?
>
Thanks!
>
Mike

(','+list.toStr ing()+',').inde xOf(','+num+',' )

If IE had implemeneted it properly you'd only need list.indexOf(nu m)

**Tom Cole** · Jun 27 '08, 07:09 PM

Re: If value is in a list

On Apr 22, 3:59 pm, "Paul Lautman" <paul.laut...@b tinternet.com>
wrote:

Mike wrote:

What about alert(num in list);- Hide quoted text -

>

Yes, that would work, but I'm actually concerned about the isInList
function. I imagine there's some way to avoid the whole for(i in
list) routine. For example, is there a way to do this:

>

function isInList( number, list ) {
if(number == anyElementIn( list ) { return true } else { return
false }
}

>

is there some built in javascript method that will check a value
against any value in an Array?

>

Thanks!

>

Mike

>
(','+list.toStr ing()+',').inde xOf(','+num+',' )
>
If IE had implemeneted it properly you'd only need list.indexOf(nu m)- Hidequoted text -
>
- Show quoted text -

You could also use RegExp:

function isInArray(value , array) {
return (new RegExp('^(' + array.join('|') + ')$').test(valu e));
}

**Paul Lautman** · Jun 27 '08, 07:09 PM

Re: If value is in a list

Tom Cole wrote:

On Apr 22, 3:59 pm, "Paul Lautman" <paul.laut...@b tinternet.com>
wrote:

>Mike wrote:

>What about alert(num in list);- Hide quoted text -

>>

Yes, that would work, but I'm actually concerned about the isInList
function. I imagine there's some way to avoid the whole for(i in
list) routine. For example, is there a way to do this:

>>

function isInList( number, list ) {
if(number == anyElementIn( list ) { return true } else { return
false }
}

>>

is there some built in javascript method that will check a value
against any value in an Array?

>>

Thanks!

>>

Mike

>>
>(','+list.toSt ring()+',').ind exOf(','+num+', ')
>>
>If IE had implemeneted it properly you'd only need
>list.indexOf(n um)- Hide quoted text -
>>
>- Show quoted text -

>
You could also use RegExp:
>
function isInArray(value , array) {
return (new RegExp('^(' + array.join('|') + ')$').test(valu e));
}

I could, but I am not the one asking for help, so I'm not likely to.

**Thomas 'PointedEars' Lahn** · Jun 27 '08, 07:09 PM

Re: If value is in a list

Mike wrote:

I have a list of numbers, e.g., (1,3,4,5,8,16,2 0), and am trying to
create a simple IF statement to see if the value is in that list. Is
there an easier or more efficient way, than the sample code below, to
do it?
>
=====
>
<script type="text/javascript">
num = 2;
list = [1,3,4,5,8,16,20];

You should declare all your identifiers. For those which should be
variables, e.g.

var num = 2;

if(isInList( num, list )) {
alert("It's there!");
} else {
alert("It's NOT there!");
}
>
function isInList( num, list ) {
// List is an Array()
result = false;

There. You create a *globally* available property, if that. Bad.

for(i in list) {
if(num == list[i]) { result = true }
}
return result
}

This would work for numeric values, but it would be inefficient, and
error-prone. Note a) that you can stop looping once you have found an item,
b) that `==' performs implicit type conversion, and c) that for..in
iteration is not equivalent to C-style `for' iteration (it iterates over the
list of all enumerable properties, not just those designating
array/collection elements). Use instead

/**
* @param number num
* @param Array list
*/
function inArray(num, list)
{
var result = false;

for (var i = list.length; i--;)
{
if (list[i] === num)
{
result = true;
break;
}
}

return result;
}

JavaScript 1.6+ also supports a native method:

list.indexOf(nu m) >= 0

Array.prototype.indexOf()

http://developer.mozilla.org/en/docs/Core_JavaScript_1.5_Reference:Global_Objects:Array:indexOf

The indexOf() method of Array instances returns the first index at which a given element can be found in the array, or -1 if it is not present.

PoinedEars

**Thomas 'PointedEars' Lahn** · Jun 27 '08, 07:09 PM

Re: If value is in a list

Mike wrote:

>What about alert(num in list);- Hide quoted text -

>
Yes, that would work, [...]

No, it would not. This expression evaluates to `true' if the value of
`num' is the name of a property of the object referred to by `list'. So

2 in [1, 2]

evaluates to `false' even though `2' is clearly an element in `[1, 2]':

[1, 2][2]

or equally

[1, 2]["2"]

is undefined as there is no third element (with index 2).

Therefore, what could work is to use the array elements as property names
for an Object object, and then apply the `in' operation on the latter:

var list = [1, 2];
var o = {};

for (var i = list.length; i--;)
{
o[list[i]] = true;
}

// true
2 in o

Note that the `in' operation, unlike for..in iteration, requires JavaScript
1.4, JScript 5.0, ECMAScript Ed. 3.

See also http://PointedEars.de/es-matrix/

Please don't remove the attribution line next time.

PointedEars
--
var bugRiddenCrashP ronePieceOfJunk = (
navigator.userA gent.indexOf('M SIE 5') != -1
&& navigator.userA gent.indexOf('M ac') != -1
) // Plone, register_functi on.js:16

**Thomas 'PointedEars' Lahn** · Jun 27 '08, 07:09 PM

Re: If value is in a list

Paul Lautman wrote:

Mike wrote:

>[...] For example, is there a way to do this:
>>
>function isInList( number, list ) {
> if(number == anyElementIn( list ) { return true } else { return
>false }
>}
>>
>is there some built in javascript method that will check a value
>against any value in an Array?
>[...]

>
(','+list.toStr ing()+',').inde xOf(','+num+',' )

Good idea, but this really only works for arrays that have serializable
values as elements. One can implement general serialization by overwriting
Object.prototyp e.toString() (without breaking for..in iteration), but only
enumerable properties and non-enumerable properties of which the names are
known can be included.

If IE had implemeneted it properly you'd only need list.indexOf(nu m)

Array.prototype .indexOf() is a proprietary JavaScript 1.6+ feature not
specified in ECMAScript, so it is pointless to say that IE did not implement
it properly. It is even more pointless because it would not have to be
IE/MSHTML but Microsoft JScript to implement it.

Please trim your quotes, especially don't quote signatures.

PointedEars
--
var bugRiddenCrashP ronePieceOfJunk = (
navigator.userA gent.indexOf('M SIE 5') != -1
&& navigator.userA gent.indexOf('M ac') != -1
) // Plone, register_functi on.js:16

**Thomas 'PointedEars' Lahn** · Jun 27 '08, 07:09 PM

Re: If value is in a list

Paul Lautman wrote:

(','+list.toStr ing()+',').inde xOf(','+num+',' )

BTW,

(',' + list + ',').indexOf(', ' + num + ',')

suffices as string concatenation implicitly calls
String.prototyp e.toString() on its non-string operands.

PointedEars
--
Prototype.js was written by people who don't know javascript for people
who don't know javascript. People who don't know javascript are not
the best source of advice on designing systems that use javascript.
-- Richard Cornford, cljs, <f806at$ail$1$8 300dec7@news.de mon.co.uk>

**Thadeu de Paula** · Jun 27 '08, 07:09 PM

Re: If value is in a list

On Apr 22, 8:39 pm, Thomas 'PointedEars' Lahn <PointedE...@we b.de>
wrote:

Paul Lautman wrote:

(','+list.toStr ing()+',').inde xOf(','+num+',' )

>
BTW,
>
(',' + list + ',').indexOf(', ' + num + ',')
>
suffices as string concatenation implicitly calls
String.prototyp e.toString() on its non-string operands.
>
PointedEars
--
Prototype.js was written by people who don't know javascript for people
who don't know javascript. People who don't know javascript are not
the best source of advice on designing systems that use javascript.
-- Richard Cornford, cljs, <f806at$ail$1$8 300d...@news.de mon.co.uk>

People...
lest use the things for the ends that they was created!
What's the problem using for?! Usign RegExp... you'll need to turn the
list into a string... it's an unnecessary step.

function arrayMember (value,list) {
for (var i in list) if (list[i]===value)
return i;
break;
};
return false;
}

This is good for biiiiiiigger lists, once it break! :D
And you will have what can be a useful info: the index!

---
About prototype, scriptaculous, jquery, etc...
I don't like to use them... I prefer do little specific libs and put
on my code when necessary...
I dislike to use excessive object abbreviations.. . but, I think, even
with these I can learn something.

That's the spirit!

**Thadeu de Paula** · Jun 27 '08, 07:09 PM

Re: If value is in a list

On Apr 22, 10:47 pm, Thadeu de Paula <thadeudepa...@ gmail.comwrote:

On Apr 22, 8:39 pm, Thomas 'PointedEars' Lahn <PointedE...@we b.de>
wrote:
>
>
>

Paul Lautman wrote:

(','+list.toStr ing()+',').inde xOf(','+num+',' )

>

BTW,

>

(',' + list + ',').indexOf(', ' + num + ',')

>

suffices as string concatenation implicitly calls
String.prototyp e.toString() on its non-string operands.

>

PointedEars
--
Prototype.js was written by people who don't know javascript for people
who don't know javascript. People who don't know javascript are not
the best source of advice on designing systems that use javascript.
-- Richard Cornford, cljs, <f806at$ail$1$8 300d...@news.de mon.co.uk>

>
People...
lest use the things for the ends that they was created!
What's the problem using for?! Usign RegExp... you'll need to turn the
list into a string... it's an unnecessary step.
>
function arrayMember (value,list) {
for (var i in list) if (list[i]===value)
return i;
break;
};
return false;
>
}
>
This is good for biiiiiiigger lists, once it break! :D
And you will have what can be a useful info: the index!
>
---
About prototype, scriptaculous, jquery, etc...
I don't like to use them... I prefer do little specific libs and put
on my code when necessary...
I dislike to use excessive object abbreviations.. . but, I think, even
with these I can learn something.
>
That's the spirit!

Oppps... there something wrong.. sorry!

function arrayMember (value,list) {
for (var i in list) if (list[i]===value) {
return i;
break;
};
return false;
};

**Thomas 'PointedEars' Lahn** · Jun 27 '08, 07:09 PM

Re: If value is in a list

Thadeu de Paula wrote:

function arrayMember (value,list) {
for (var i in list) if (list[i]===value) {
return i;
break;
};
return false;
};

This is error-prone for the reasons I gave in
<news:480E665B. 6050506@Pointed Ears.de>

Please trim your quotes, see http://jibbering.com/faq/ pp.

PointedEars
--
Prototype.js was written by people who don't know javascript for people
who don't know javascript. People who don't know javascript are not
the best source of advice on designing systems that use javascript.
-- Richard Cornford, cljs, <f806at$ail$1$8 300dec7@news.de mon.co.uk>

If value is in a list

If value is in a list

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