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08-15-2005, 08:41 AM
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Posts: 37
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Array within an Array: Possible?
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This is just a theoretical topic and meant to encourage discussion, not a "HELP ME" topic.
NESTED ARRAYS:
Ok, a confusing subject to be sure, but I'm wondering, is it possible to store the entire contents of a single dimensional array within one element of another array. A simple example would be as follows:
Code:
Dim MyArray(5) as Variant, Test(3) as Variant
Test(0) = 6
Test(1) = 10
Test(2) = 99
MyArray(0) = 150
MyArray(1) = 250
MyArray(2) = Test
MyArray(3) = 400
MyArray(4) = 500
The resulting data table would look similar to this:
Code:
MyArray 1 --- 150
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MyArray 2 --- 250
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My Array 3 -------- Test --- 6
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| Test --- 10
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| Test --- 99
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My Array 4 --- 400
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My Array 5 --- 500
So, calling MyArray(3) would return what? An error? All three values? Some weird mishmash of unreliable data?
I believe Pearl has this ability to store arrays within arrays ... but don't quote me on that.
I also know that AutoIt has this ability, see this link to read the discussion about it, but it's more of an "undocumented and unintended feature that happens to work" |
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The Blue Drache
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08-15-2005, 09:06 AM
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Posts: 397
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Well, you can do that with variants.
ie
Code:
Dim foo() As Variant
Dim bar() As Variant
Dim blah() As Variant
ReDim foo(1 To 2)
foo(1) = "Hi"
foo(2) = 0.8767
ReDim bar(1 To 2)
bar(1) = "Maybe"
bar(2) = foo
blah = bar(2)
MsgBox CStr(blah(1))
And that extends to multi-dimensions too. foo could be a 5-D array. The only difference is that the line MsgBox Cstr(blah(1) would have to be MsgBox Cstr(blah(1,1,1,1,1))
All bar(2) returns is the array foo. You can do whatever you like with it.
That what you mean? |
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08-15-2005, 09:11 AM
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Quote:
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Originally Posted by BobThePenguin
Code:
Dim foo() As Variant
Dim bar() As Variant
Dim blah() As Variant
ReDim foo(1 To 2)
foo(1) = "Hi"
foo(2) = 0.8767
ReDim bar(1 To 2)
bar(1) = "Maybe"
bar(2) = foo
blah = bar(2)
MsgBox CStr(blah(1))
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Not exactly. Your code only sets the variant "blah" as a single dimensional arry with one element, and sets one element of the bar array to it.
I'm saying in a nested array, you'd set a single array element (in a single or multi-dimensional) equal to an ENTIRE single dimensional array.
Maybe
Code:
Dim blah(2) = Foo(1 to 2)
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The Blue Drache
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08-15-2005, 09:19 AM
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Quote:
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Originally Posted by Blue_Drache
Not exactly. Your code only sets the variant "blah" as a single dimensional arry with one element, and sets one element of the bar array to it.
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Check my example again, blah is a 1-D array containing 2 values. blah(1) = "Hi", blah(2) = 0.8767. You are correct that I am only setting one element of bar equal to blah. But that element of bar is the entire array foo.
ok, maybe its a little confusing, step through the example and youll see though I think.
Quote:
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I'm saying in a nested array, you'd set a single array element (in a single or multi-dimensional) equal to an ENTIRE single dimensional array.
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In my example, the single array element is bar(2). Then, this is being set equal to the ENTIRE single dimensional array foo.
The only point of blah was to show how you could get the information in foo using the array bar.
EDIT:
Ok, just learned a new way to deal with the arrays and its less confusing:
Code:
Dim foo() As Variant
Dim bar() As Variant
ReDim foo(1 To 2)
foo(1) = "Hi"
foo(2) = 0.8767
ReDim bar(1 To 2)
bar(1) = "Maybe"
bar(2) = foo
MsgBox CStr(bar(2)(1)) '*
*: here bar(2)(1) gets the second element in bar and then the first element in the array that bar(2) contains; ie foo(1) |
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08-15-2005, 10:04 AM
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Promising Talent
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Quote:
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Originally Posted by Blue_Drache
I believe Pearl has this ability to store arrays within arrays ... but don't quote me on that.
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If I would quote you, I would at least write Perl correctly.  (Unless you really mean the more obscure language Pearl, which seems unlikely.)
I don't know Perl, but a quick glance at some documentation seems to reveal that its arrays - unlike in the few languages that I do know - can not contain other arrays. But you can do this:
Code:
@a = (1,2,3);
@b = ("hello", @a, "bye"); # @b is ("hello",1,2,3,"bye")
Example taken from http://www.cs.rpi.edu/~hollingd/eiw/...erlArrays.html
As I said, arrays containing arrays are not uncommon at all. In fact, in many languages all multidimensional arrays are arrays of arrays. VB is exceptional here in that it has separate multidimensional arrays. But as BobThePenguin said, it's perfectly possible to have arrays containing arrays too. But you will rarely need it.
Quote:
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Originally Posted by BobThePenguin
Ok, just learned a new way to deal with the arrays and its less confusing:
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Your new way is the only correct way. You can't address array elements in 'arrays of arrays' as if they were ordinary multidimensional arrays, like you were implying earlier. |
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08-15-2005, 10:21 AM
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Quote:
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Originally Posted by Deadalus
Your new way is the only correct way. You can't address array elements in 'arrays of arrays' as if they were ordinary multidimensional arrays, like you were implying earlier.
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If I implyed that earlier I certainly didnt mean to and I cant really see where I did. Since I've never actually had any call to use arrays like this I was only aware of how it could be done. I didnt know that you could reference the elements in the sub array like tmp(1)(1) so I just posted what occured to me at the time, thats why I had the line blah = bar(2). This does accomplish the goal of letting you view the information in bar(2), it is just a clumsy workaround when you dont know that bar(2)(1) will work. |
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08-15-2005, 11:07 AM
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Ultimate Contributor
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Another example of arrays within arrays could be use of UDTs. Here is a simple example. Usage: Rare.
Code:
Private Type ArrayUDT
arrElements() As Integer ' string,long,variant,whatever
End Type
Private ArrayOfArrays() As ArrayUDT
Private Sub SomeName()
' example only. Contain 2 arrays (100 & 200 elements) in a single array
ReDim Preserve ArrayOfArrays(0 To 1) ' can also be multideminsion
Dim I As Integer, J As Integer
For I = 0 To UBound(ArrayOfArrays)
' redim the subarray & populate it with sample data
ReDim ArrayOfArrays(I).arrElements(0 To (I + 1) * 100)
For J = 0 To (I + 1) * 100
ArrayOfArrays(I).arrElements(J) = J
Next
Next
End Sub
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08-15-2005, 12:02 PM
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Sure, you can create arrays of arrays.
I mention this in the arrays installment of Standards & Practices Tutorial
In addition, a while back, in a reply to a thread on file processing, I demonstrated a use for (and how to set it up.) The example project is attached. |
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08-15-2005, 01:10 PM
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An array within an array is essentially a 2D array, and an array within that is a 3D array etc. The only difference is that only one element would be 2D if you only put one array element in it.
I also know that in PHP, that is how you are supposed to make multi-dimensional arrays, and you can do that just fine.
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08-15-2005, 03:45 PM
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Captain Convoluted
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Just to add to the confusion, I came up with an arrays-within-arrays solution to a hypothetical problem discussed in this thread
http://www.xtremevbtalk.com/showthread.php?t=227232
(post 8)
Don't look too closely at the code that follows in post 9, it's neither pretty nor efficient  |
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08-15-2005, 04:50 PM
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Quote:
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Originally Posted by by_m
An array within an array is essentially a 2D array, and an array within that is a 3D array etc
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Ah, but an array of arrays allows you to have dynamic arrays of dynamic arrays,
Which, in turn allows you to redim preserve ALL array elements (and not just the last dimension...)
In addition, it allows you to conserver space in left justified sparse arrays.
For instance, suppose you have the following file that you need to copy each word into an array, AND you must maintain the array position of the word (Row and column position)
Quote:
This is a test of copying
words from
a file into an array of words maintaining the row and column positions
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If you specify a 2-d array, it would have to have 13 columns and 3 rows. Unfortunately, since the first line has only 5 words, you would have 8 "empty cells" in the first row, and 11 empty cells in the second row, since you need to size the array to hold the maximum "width."
If you create a dynamic array of dynamic arrays, however, you could redim each sub-array to the correct size needed. No muss, no fuss, and no empty array elements. |
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Last edited by loquin; 08-15-2005 at 05:03 PM.
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08-15-2005, 06:30 PM
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Truly so, good stuff. I have to say that I really like PHP arrays...and I like them even more now.
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10-20-2005, 01:25 PM
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This is a great discussion. It reminds me of one we had over C# arrays here at work, but that turned into a heated argument, then a little yelling, and there were police dogs...
Anyway. What's the most arrays any developer would need, anyway? I've never used more than four dimensions, and that was only for a project I was handing off, and I wanted the nesting to be absolutely horrifying. Do we really need a language to offer unlimited arrays within arrays?
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10-20-2005, 01:49 PM
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Excellent…
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I would be hesitant to equate a 2d array to an array of arrays, it seems to me that they’re quite different.
The following might help to show why, if you own Excel (this relies on Excel's Evaluate Method, do not attempt this specific code in VB6, Word, etc... Without binding to Excel), try the following in Excel's IDE:
Code:
Sub foo()
Dim x() As Variant
Let x = Array([{1,2,3;4,5,6}], _
[{"test1","test2","test3";1,2,3}])
Debug.Print x(0)(1, 2), x(0)(2, 2)
Debug.Print x(1)(1, 1), x(1)(2, 1)
End Sub
This gives us an a 1d array of 2d arrays, as you can see. Note that the Evaluate Method coerces the Array to a 1-based Array in the sub-arrays. And the indexing is that of the Matrix (a spreadsheet), the first array lines up as such:
1 2 3
4 5 6
So you reference your vectors as (element)(element row, element column). |
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