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Associative array

P: n/a
I am curious why some people feel that Javascript doesn't have
associative arrays. I got these definitions of associative arrays via
goggle:

Arrays in which the indices may be numbers or strings, not just
sequential integers in a fixed range.
http://www.sunsite.ualberta.ca/Docum...r/gawk_20.html

(n.) A collection of data (an array) where individual items can be
indexed (accessed) by a string, rather than by an integer as is common
in most programming languages.
docs.sun.com/db/doc/805-4368/6j450e60a

(n.) A collection of data (an array) where individual items may be
indexed (accessed) by a string, rather than by an integer as is common
in most programming languages.
www.npac.syr.edu/nse/hpccgloss/hpccgloss.html

Another name for a dictionary.
academics.tjhsst.edu/compsci/thinkCS/chap19/node11.html
My goggle search:
http://www.google.com/search?hl=en&l...ociative+Array
It seems to me that both javascript arrays and object meet these
definitions.

One problem with Javascript would be the extra indexes automatically
created but you can check for them if you need too.
Maybe I am missing something.

Robert

Jul 23 '05 #1
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4 Replies


P: n/a
Robert wrote:
I am curious why some people feel that Javascript doesn't have
associative arrays.


Because Javascript, JScript nor ECMAScript have associative arrays.

Pretty good reason don't you think?

--
Randy
comp.lang.javascript FAQ - http://jibbering.com/faq
Jul 23 '05 #2

P: n/a
On 9 Dec 2004 15:09:07 -0800, Robert <rc*******@my-deja.com> wrote:
I am curious why some people feel that Javascript doesn't have
associative arrays.
The behaviour has nothing to do with arrays. The misconception arises
because "associative arrays" are introduced thus:

var arr = new Array();

arr['name'] = 'value';

However, you can't apply any Array method to that object and expect it to
act upon 'name' as it's not part of the array; it's part of the object
itself. The same outcome is achieved with:

arr.name = 'value';

The main difference between the two approaches is that with dot notation,
each token must conform to the rules of an identifier. With square bracket
notation, the operand is any valid expression.

I presume that many script authors are unaware that you can use square
brackets to construct property names because the fact that this is what
you're actually doing - accessing object properties - is never discussed.
It's hidden among this illusion.

The fact of the matter is: ECMAScript does not have them. To produce a
robust system of storage you have to write at least *some* supporting
code, which immediately draws attention to the fact that ECMAScript
doesn't provide this functionality natively.

If it helps in some way to think of associative arrays, fine. However,
make sure you know what is really happening behind the scenes.

[snip]
docs.sun.com/db/doc/805-4368/6j450e60a
When posting URLs, please post them in full. Preferably surrounded by
<URL:...>:

<URL:http://docs.sun.com/db/doc/805-4368/6j450e60a>

[snip]
It seems to me that both javascript arrays and object meet these
definitions.
Loosely, perhaps. However, these terms are applied to languages which
feature arrays that can be indexed by strings and numbers. You just aren't
doing that with ECMAScript: an array is *just* an array.
One problem with Javascript would be the extra indexes automatically
created
[Aside]
It's interesting to see you refer to the "extra indexes". Either that's a
Freudian slip, or potential proof of the misconception I mentioned earlier.
[/Aside]
but you can check for them if you need too.


How? You can't enumerate them, and you can never be sure of all of the
properties and methods that will be present. It's best to avoid the issue
entirely by modifying the name you use so that it will never clash with an
existing property.

[snip]

Mike

--
Michael Winter
Replace ".invalid" with ".uk" to reply by e-mail.
Jul 23 '05 #3

P: n/a
"Michael Winter" <M.******@blueyonder.co.invalid> wrote:
The behaviour has nothing to do with arrays. The misconception arises
because "associative arrays" are introduced thus:

var arr = new Array();

arr['name'] = 'value';


Maybe one can show the misconception like this:

var arr = new Array();

(1) arr['name'] = 'value';

Now it looks like one added a key/value pair to a hash.

Array() has methods like pop() or push(), lets give the "hash datatype"
some as well.

(2) arr['keys'] = getkeys; // function defined elsewhere
// The same as arr.keys = getkeys

so now, arr.keys() should get the keys of the hash.

But wait:

arr['foo'] = bar is the way to add a key/value pair.

So (2) should just do this and the hash should contain

'name' = 'value'
'keys' = getkeys

But this is wrong as well.

'keys' should not be a data of the hash. It should be a method like
pop() for accessing the data of a hash.

And yes, it is perfectly OK for a hash to hold functions.
So this is a conflict it the alleged semantics of these
assignment. The reason for the conflict is, that there is no native
hash type in Javascript.

Bye,
Martin
Jul 23 '05 #4

P: n/a
In article <11**********************@z14g2000cwz.googlegroups .com>,
Robert <rc*******@my-deja.com> writes
I am curious why some people feel that Javascript doesn't have
associative arrays.
One reason is that there are two meanings and no-one knows which is
being used. 'Associative array' can describe a very general kind of
storage unit, just as 'stack' can be a very general description.
Alternatively, 'associative array' can be a particular data type
supplied as part of a computer language. You can get some lovely
never-ending arguments if people are using these different meanings.

I got these definitions of associative arrays via
goggle:

Arrays in which the indices may be numbers or strings, not just
sequential integers in a fixed range.
http://www.sunsite.ualberta.ca/Docum...r/gawk_20.html

(n.) A collection of data (an array) where individual items can be
indexed (accessed) by a string, rather than by an integer as is common
in most programming languages.
docs.sun.com/db/doc/805-4368/6j450e60a

(n.) A collection of data (an array) where individual items may be
indexed (accessed) by a string, rather than by an integer as is common
in most programming languages.
www.npac.syr.edu/nse/hpccgloss/hpccgloss.html
Back in the 60s when people were discussing hardware associative arrays
the 'address', or key, or index, was just a bit pattern supplied by the
user. The user might think it was ASCII characters or a floating point
number or whatever, but the hardware couldn't care less.

When an associative array is implemented in software the 'address' has
to be a defined type so the compiler/interpreter knows how to allocate
the right amount of storage when creating a cell, but it still isn't
restricted to integers and strings.

Another name for a dictionary.
academics.tjhsst.edu/compsci/thinkCS/chap19/node11.html
A dictionary is a particular kind of associative array. The 'address' is
a word; the value is a chunk of text.

But then people have used 'dictionary' in a more general way. 'Map' is
another popular name.

My goggle search:
http://www.google.com/search?hl=en&l...ociative+Array
It seems to me that both javascript arrays and object meet these
definitions.

One problem with Javascript would be the extra indexes automatically
created but you can check for them if you need too.
Maybe I am missing something.


True. Both Object objects and Array objects have their good points and
their bad points if your javascript application needs to implement an
associative array.

John
--
John Harris
Jul 23 '05 #5

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