Best way to find if item is in array?

J. B. Moreno · Aug 31, 2005

What's the best (i.e. fastest) way to find out if an array contains a given
value? Other than looping, the only way I know to do it is to use an
associative array/hash instead....

Is there a better/faster way?

I.e if I have a list of names, what's the best way to find out if the aray
contains "jane"?

ASM · Aug 31, 2005

J. B. Moreno said:
What's the best (i.e. fastest) way to find out if an array contains a given
value? Other than looping, the only way I know to do it is to use an
associative array/hash instead....

Is there a better/faster way?

I.e if I have a list of names, what's the best way to find out if the aray
contains "jane"?

don't know if is better ?

alert(myArray.join.indexOf(myValue));

J. B. Moreno · Aug 31, 2005

ASM said:
don't know if is better ?

alert(myArray.join.indexOf(myValue));

I think I understand that, but let me test my understanding:
It joins the array into a string, and then searches inside the string
for the given value? So, if for instance I had myArray = new
Array("frank", "jim'n'jane"); and did
alert(myArray.join.indexOf("jane")); it would find it?

That's not actually a show stopper in this case...but I might have to do
some test to see if it's actually faster.

Anyway, thanks for the alternative

McKirahan · Aug 31, 2005

J. B. Moreno said:
I think I understand that, but let me test my understanding:
It joins the array into a string, and then searches inside the string
for the given value? So, if for instance I had myArray = new
Array("frank", "jim'n'jane"); and did
alert(myArray.join.indexOf("jane")); it would find it?

That's not actually a show stopper in this case...but I might have to do
some test to see if it's actually faster.

Anyway, thanks for the alternative

ASM · Aug 31, 2005

error ! have had to read :

alert(myArray.join().indexOf(myValue));

I think I understand that, but let me test my understanding:
It joins the array into a string, and then searches inside the string
for the given value? So, if for instance I had myArray = new
Array("frank", "jim'n'jane"); and did
alert(myArray.join.indexOf("jane")); it would find it?

no

if it finds it returns '1'
if not it returns '-1'

so for true/false :

alert(myArray.join().indexOf(myValue)>=0)

that's to say :

if(myArray.join().indexOf(myValue)>=0) alert('true');
else alert('false');

That's not actually a show stopper in this case...but I might have to do
some test to see if it's actually faster.

a demo ?

<html>
<script type="text/javascript">

tbl = new Array("frank", "jim'n'jane", "moriaux", "toto", "foo");
arr = new Array('potato','salade','pear','orange','apple',banana');

alert(tbl.join().indexOf('ri')>=0);
alert(tbl.join().indexOf('st')>=0);
alert('results must have been :\n true\nfalse');

function verif(myArray,myValue) {
var yesno = eval(myArray).join().indexOf(myValue)>=0;
return yesno;
}

document.write('array = "tbl"<br>content = '+tbl.join()+
'<br>array = arr<br>'+arr.join());
</script>
<form onsubmit="alert(verif(I1.value,I2.value));return false;">
<p>Enter array's name : <input name="I1" value="tbl">
Enter search value : <input name="I2" value="">
<hr><p align=center><input type=submit value="verify">
<input type=reset value="reset">
</form>
</html>

Jim Davis · Aug 31, 2005

Change
alert(myArray.join.indexOf("jane"));
to
alert(myArray.join().indexOf("jane"));

To ensure that your search string is not embedded try this:

var myJoin = "|" + myArray.join("|") + "|";
alert(myJoin.indexOf("|frank|"));
alert(myJoin.indexOf("|jane|"));

This presumes that "|" is not a character in your array.

In general, unless your array is very large or you search it a lot, a
client-side loop is just so damn fast why bother playing games?

And if it IS very large or you search it a lot why not set up a hash table?
Then it's just "if ( myHash["Jane"] ) {};" Instant results with no fuss.

Just my opinion of course - which doesn't change the fact that McKirahan's
solution will, indeed, work just fine. ;^)

Jim Davis

ASM · Aug 31, 2005

Jim said:
And if it IS very large or you search it a lot why not set up a hash table?
Then it's just "if ( myHash["Jane"] ) {};" Instant results with no fuss.

Just my opinion of course - which doesn't change the fact that McKirahan's
solution will, indeed, work just fine. ;^)

tbl = new Array("frank", "jim'n'jane", "moriaux", "toto", "foo");

alert(tbl['toto']);

returns : undefined

Evertjan. · Aug 31, 2005

ASM wrote on 31 aug 2005 in comp.lang.javascript:

Jim said:
Jim said:

And if it IS very large or you search it a lot why not set up a hash
table? Then it's just "if ( myHash["Jane"] ) {};" Instant results
with no fuss.

Just my opinion of course - which doesn't change the fact that
McKirahan's solution will, indeed, work just fine. ;^)

Click to expand...

tbl = new Array("frank", "jim'n'jane", "moriaux", "toto", "foo");

alert(tbl['toto']);

returns : undefined

var tbl = {"frank":1, "jim'n'jane":1,
"moriaux":1, "toto":1, "foo":1};

alert(tbl['toto']); // 1

alert(tbl['blahblah']); // undefined

Jim Davis · Aug 31, 2005

ASM said:
Jim said:

And if it IS very large or you search it a lot why not set up a hash
table? Then it's just "if ( myHash["Jane"] ) {};" Instant results with
no fuss.

Just my opinion of course - which doesn't change the fact that
McKirahan's solution will, indeed, work just fine. ;^)

Click to expand...

tbl = new Array("frank", "jim'n'jane", "moriaux", "toto", "foo");

alert(tbl['toto']);

returns : undefined

I'm sorry... I think you've missed something. This isn't a hash table so it
would, of course, return "undefined".

A "normal" array, as you've built, is indexed by a count (numbers) -
1,2,3,4,5,etc. You can access any element by it's numerical position in the
array (JavaScript also supports numerically indexed arrays where the numbers
are not in order, but leave them out of the discussion for now). You can do
"MyArray[1]", "MyArray[4]", etc. You can loop over the array easily using a
counter loop.

A hash table can be most easily thought (at least by me) of an array indexed
by values (the values can be anything: strings, object references,
whatever). In many languages these values are called "keys" and in
JavaScript they're object properties. You would access values by
"MyHash[MyKeyValue]" (just as you would access any object property using
bracket notation).

So, to demonstrate, try this:

tbl = {"frank": null, "jim'n'jane": null, "moriaux": null, "toto": null,
"foo": null}

This (object literal notation) will create an object where each property is
the "name" and the value is "null". If you need access to array methods in
your hash (most of the time you don't) you might also do this:

tbl = new Array();
tbl["frank"] = null;
tbl["jim'n'jane"] = null;
tbl["moriaux"] = null;
tbl["toto"] = null;
tbl["foo"] = null;

(But, as noted elsewhere, you cannot use any existing array properties -
namely "length" as a key name.)

In either case however try alert(tbl['toto']); again.

This is a very powerful aspect of the language that just doesn't get use "in
the wild".

Jim Davis

Copy string from 2D array to a 1D array in C	1	Nov 1, 2023
Program to find the largest integer element of an array.	1	Mar 2, 2022
Trying to return true if a sub array exists at given index	1	Mar 4, 2021
Hello guys ! How do I convert a string from an array into numbers ? Javascript	3	Dec 19, 2022
FOSS or Freeware, Prefferably Runs on Linux Mint: Search US Goverment Records, Legally to Find Literarary Work	8	Apr 5, 2023
Accessing array index addresses with custom datatype in a function	0	Jun 2, 2022
Best way to find starting directory	0	Mar 19, 2013
Select Eof extension files based on text list of filenames with if condition	0	May 4, 2022

Best way to find if item is in array?

J. B. Moreno

ASM

J. B. Moreno

McKirahan

ASM

Jim Davis

ASM

Evertjan.

Jim Davis

Ask a Question

Similar Threads

Members online

Forum statistics

Latest Threads