Nested or Multidimensiona l Arrays

[TheKeith]

I can't figure out why this doesn't work:

---------------------------------------------
greeting = new Array();

greeting[0][0] = "hey";
greeting[0][1] = "bye";
trace(greeting[0][0] + greeting[0][1]);

---------------------------------------------

Shouldn't this automatically create a multidimensiona l array? Can someone
help me? Thanks.

[TheKeith]

sorry I forgot to mention that the trace part is because it's something I'm
actually doing in actionscript, but since actionscriptis based on
javascript, I figured I could get a good answer here too.

"TheKeith" <[e-mail]> wrote in message
news:9b******** ************@gi ganews.com...

I can't figure out why this doesn't work:

---------------------------------------------
greeting = new Array();

greeting[0][0] = "hey";
greeting[0][1] = "bye";
trace(greeting[0][0] + greeting[0][1]);

---------------------------------------------

Shouldn't this automatically create a multidimensiona l array? Can someone
help me? Thanks.

[Michael Winter]

On Sat, 3 Apr 2004 15:02:37 -0500, TheKeith <[e-mail]> wrote:

greeting = new Array();

greeting[0][0] = "hey";
greeting[0][1] = "bye";

Shouldn't this automatically create a multidimensiona l array? [...]

No, it shouldn't.

An array is just an array, and with "= new Array()" or "= []", all of its
elements are undefined. As such, using myArray[ index ] will return
undefined, and attempting to subscript that is simply an error.

You'll have to assign an array to each element of the original array to
make a multi-dimensional array. You could either do this explicitly, or
write two functions; one to set, and the other to get elements at the
given indicies. They could check if the sub-array exists within the first,
and if not, create it before assigning a value to it. Similarly, if the
sub-array doesn't exist when trying to get a value, return undefined but
without causing an error (by not actually accessing a non-existent array).

Mike

--
Michael Winter
M.******@blueyo nder.co.invalid (replace ".invalid" with ".uk" to reply)

[Richard A. DeVenezia]

TheKeith wrote:

Shouldn't this automatically create a multidimensiona l array? Can
someone help me? Thanks.

I use this helper function to create (and debug) multi-dimensional arrays.

//====== Multidimensiona l array

function MDArray (dimensions) {
// instantiate objects representing a multi dimensional array
// dimensions - array of numbers, ith number is nunmber of elements in
dimension i

this.length = dimensions[0]
this.dimensions = dimensions
if (dimensions.len gth>0) {
for (var i=0;i<this.leng th;i++) {
this[i] = new MDArray(dimensi ons.slice(1))
}
}
}
MDArray.prototy pe = new Array()
MDArray.prototy pe.constructor = MDArray
MDArray.prototy pe.toHTML = function(addr) {
var html = ''
if (this.dimension s.length > 2) {
for (var i=0;i<this.dime nsions[0];i++) {
html += this[i].toHTML((addr?a ddr+',':'')+i)
}
}
else
if (this.dimension s.length == 2) {

html += '<BR>'+argument s[0]+'<TABLE BORDER=1>'
for (var i=0;i<this.dime nsions[0];i++) { html += '<TR>'
for (var j=0;j<this.dime nsions[1];j++) { html += '<TD>'
html += this[i][j] + '</TD>'
} html += '</TR>'
} html += '</TABLE>'
}
else {
html = this.toString()
} return html
}

mda = new MDArray([4,4,4,4])
mda[0][0][0][0] = 0
mda[1][1][1][1] = 1
mda[2][2][2][2] = 2
mda[3][3][3][3] = 4
document.write (mda.toHTML())

--
Richard A. DeVenezia
http://www.devenezia.com/downloads/sas/macros/?m=xmlib

[TheKeith]

"Michael Winter" <M.******@bluey onder.co.invali d> wrote in message
news:op******** ******@news-text.blueyonder .co.uk...

On Sat, 3 Apr 2004 15:02:37 -0500, TheKeith <[e-mail]> wrote:

greeting = new Array();

greeting[0][0] = "hey";
greeting[0][1] = "bye";

Shouldn't this automatically create a multidimensiona l array? [...]

No, it shouldn't.

An array is just an array, and with "= new Array()" or "= []", all of its
elements are undefined. As such, using myArray[ index ] will return
undefined, and attempting to subscript that is simply an error.

You'll have to assign an array to each element of the original array to
make a multi-dimensional array. You could either do this explicitly, or
write two functions; one to set, and the other to get elements at the
given indicies. They could check if the sub-array exists within the first,
and if not, create it before assigning a value to it. Similarly, if the
sub-array doesn't exist when trying to get a value, return undefined but
without causing an error (by not actually accessing a non-existent array).

thanks a lot Mike, I got it working ok now.

[TheKeith]

"Richard A. DeVenezia" <ra******@ix.ne tcom.com> wrote in message
news:c4******** *****@ID-168040.news.uni-berlin.de...

TheKeith wrote:

Shouldn't this automatically create a multidimensiona l array? Can
someone help me? Thanks.

I use this helper function to create (and debug) multi-dimensional arrays.

//====== Multidimensiona l array

function MDArray (dimensions) {
// instantiate objects representing a multi dimensional array
// dimensions - array of numbers, ith number is nunmber of elements in
dimension i

this.length = dimensions[0]
this.dimensions = dimensions
if (dimensions.len gth>0) {
for (var i=0;i<this.leng th;i++) {
this[i] = new MDArray(dimensi ons.slice(1))
}
}
}
MDArray.prototy pe = new Array()
MDArray.prototy pe.constructor = MDArray
MDArray.prototy pe.toHTML = function(addr) {
var html = ''
if (this.dimension s.length > 2) {
for (var i=0;i<this.dime nsions[0];i++) {
html += this[i].toHTML((addr?a ddr+',':'')+i)
}
}
else
if (this.dimension s.length == 2) {

html += '<BR>'+argument s[0]+'<TABLE BORDER=1>'
for (var i=0;i<this.dime nsions[0];i++) { html += '<TR>'
for (var j=0;j<this.dime nsions[1];j++) { html += '<TD>'
html += this[i][j] + '</TD>'
} html += '</TR>'
} html += '</TABLE>'
}
else {
html = this.toString()
} return html
}

mda = new MDArray([4,4,4,4])
mda[0][0][0][0] = 0
mda[1][1][1][1] = 1
mda[2][2][2][2] = 2
mda[3][3][3][3] = 4
document.write (mda.toHTML())

--
Richard A. DeVenezia
http://www.devenezia.com/downloads/sas/macros/?m=xmlib

Thanks a lot, Richard, but it's a little more than I needed to do. I just
realized that I needed to initiate a new instance of the nested array:

array1[1] = new Array();

--that works fine for me.