2D Array [RESOLVED]

[twisted]

I am trying to create an 2D array using these values:

'                   Boston   Chicago    Dallas  Las Vegas   Los Angeles Miami   Washington D.C  
' Boston            0        1004       1753    2752        3017        1520    448
' Chicago           1004     0          921     1780        2048        1397    709
' Dallas            1753     921        0       1230        1399        1343    1307
' Las Vegas         2752     1780       1230    0           272         2570    2420
' Los Angeles       3017     2048       1399    272         0           2716    2646
' Miami             1520     1397       1343    2570        2716        0       1057
' Washington D.C.   448      709        1307    2420        2646        1057    0

Am I starting this out right??

Dim dblMileage(6, 6) As Double
            dblMileage(0, 0) = 0
            dblMileage(0, 1) = 1004

[mendhak]

It doesn't matter which way you populate it, as long as you're accessing it the right way, which depends upon how you populated it! So basically, know what you're doing!


Somehow, I get the nagging feeling that there is an easier way to do what you're doing, instead of using an array.

[twisted]

Have to use an array! Then I think I'll use a For...Next statement!

[brown monkey]

like this?

Dim num(,) As Double = { _
      {0, 1004, 1753, 2752, 3017, 1520, 448}, _
      {1004, 0, 921, 1780, 2048, 1397, 709}, _
      {1753, 921, 0, 1230, 1399, 1343, 1307}, _
      {2752, 1780, 1230, 0, 272, 2570, 2420}, _
      {3017, 2048, 1399, 272, 0, 2716, 2646}, _
      {1520, 1397, 1343, 2570, 2716, 0, 1057}, _
      {448, 709, 1307, 2420, 2646, 1057, 0} _
      }
 
      Dim s() As String = {"boston", "chicago", "dallas", "las vegas", "los angeles", "miami", "washington d.c"}
 
      Dim i As Integer
      For i = 0 To 6
         ListView1.Items.Add(s(i))
         Dim j As Integer
         For j = 0 To 6
            ListView1.Items(i).SubItems.Add(num(i, j))
         Next
      Next

if not, i'm very very very sorry.

[taxes]

Hi twisted,

To answer your original post yes you are on the right track.
However, you can store values ONLY in the final dimension of an array - in your case in each of the 6 elements of the second dimension. All other elements of all other dimensions are simply numerical references guiding you to the final storage element, so you will not be able to store names in the first dimension.

Therefore, provided you intend to allocate the names of the cities to specific elements of the array then you are correct.

i.e. in dblarray(0,1), the 0 wil REFER to Boston as on the left hand, verticle view and the 1 will HOLD the distance relating to Chicago as in the top line horizontal view, etc.

However, if you have to make provision for adding other cities, then you will need 2 two dimensional arrays.

dblarray1( , 0) where the 0 will contain the name of a city
dblarray2( , ) which will act exactly as your present array

[mendhak]

Taxes:

Is there an easier way to store that kind of information? I am curious to know.

[taxes]

Originally posted by mendhak
Taxes:

Is there an easier way to store that kind of information? I am curious to know.

I personally don't think so. There are several other ways but if you look at his various posts, this guy is completing elementery assignments. I doubt if he has even looked at database or spreadsheet access yet. What we are looking at is not STORING the information but ACCESSING it. We are not even considering how it should be displayed or entered. I would hate to suggest to him that he creates a new class to hold the data in a collection

What are your views?

[mendhak]

That sounds pretty good too, except for the amount of work to be put in, I guess.

My first guess was to create a class with three properties: FromCity, ToCity, Distance.

After that, add a bit of logic:

If FromCity and ToCity are the same, then Distance = 0.

Also, when calling the function to determine the distance between FromCity and ToCity, it shouldn't matter if FromCity and ToCity have been entered in the correct order. Let the logic do that... that should also eliminate half the entries too.

Catch my drift?

But again, I'm not too sure about this. I am going to try this out. If it's too much work, I'll abandon it

[taxes]

Originally posted by mendhak
That sounds pretty good too, except for the amount of work to be put in, I guess.

My first guess was to create a class with three properties: FromCity, ToCity, Distance.

If you consider this for a moment, you are going to have to create an instance of the class for each possible combination - in the case of 6 cities that means 25 instances.

If you have a fixed number of cities, you class properties could be
FromCity, ToCity1, Distance1, ToCity2, Distance2 etc.

I think the array approach is better in this case.

[PT Exorcist]

Originally posted by taxes
I personally don't think so. There are several other ways but if you look at his various posts, this guy is completing elementery assignments. I doubt if he has even looked at database or spreadsheet access yet. What we are looking at is not STORING the information but ACCESSING it. We are not even considering how it should be displayed or entered. I would hate to suggest to him that he creates a new class to hold the data in a collection

What are your views?

Yes there is. Just use an array of structs

[mendhak]

Originally posted by taxes
If you consider this for a moment, you are going to have to create an instance of the class for each possible combination - in the case of 6 cities that means 25 instances.

If you have a fixed number of cities, you class properties could be
FromCity, ToCity1, Distance1, ToCity2, Distance2 etc.

I think the array approach is better in this case.

Yes, you're right. I just found myself turning it into a collection for this purpose. And I also noticed that it IS a lot of work, and I'm eventually using something similar to an array.

Ugh.

concepts.

[taxes]

Originally posted by PT Exorcist
Yes there is. Just use an array of structs

I would be interested to learn how that would be simpler

[twisted]

Ok Taxes you seem to know me pretty well and this is my second to last assignment for the semester. Yes I am a VB newb so here goes the questions:

I am using two ListView boxes with the same cities in each box in the same index order, the user will select one from each (which I can't figure out, right now they can only select one from either) then they will click a menu item call mnuMileage and it will calculate the mileage between the two cities. Now like you said I am doing it right like this:

Dim dblMileage(6, 6) As Double
            dblMileage(0, 0) = 0
            dblMileage(0, 1) = 1004

But where do they get the Mileage data from?? I have to set up something where it pulls out the data.

Say for dblMileage (0,3) that would be from Boston to Dallas.

dblMileage (0, 3) would equal 1753 but how does it pull out this information and from what??

[taxes]

Hi,

YOU have to decide from where to get the mileage data

When you are writing the program you have to decide that in dblMileage(x , y), y contains the number of miles between the cities denoted by x and y.

Now, you can do this in two ways (apart from using a link to the GPS )

1. You can import the data from a database (which is what you will do when you become more proficient)

OR

2. You can write the mileage in yourself at design time. e.g.

If Boston is your first city and Chicago your second and the mileage is 1004, then when loading your form you include the code:


dblMileage(0,1)=1004
dblmileage(1,0)=1004

etc.

Now, when the city selections have been made from the two listviews, you obtain the result by:

dblMileage(x,y)

Where x= the ListView1.SelectedIndex and
y= the ListView2.SelectedIndex.

You have to be careful that you do not change the sort order in the ListView from the order of cities used in the array.

Is that what you want or have I misunderstood you?

By the way, unless you are a geographical genius, there is no way you will write a programme which actually CALCULATES the distance between two cities. All you will be doing is to DISPLAY the distance you have previously determined (probably by looking up someone else's figures )

[twisted]

That's exactly what I needed to know.

Also right now I can only select a city from lstDet or lstDep. I want to select a city from each one. Do you know why this is happening? They are two different ListView boxes so I should be able to select an item for each one right.

[taxes]

Originally posted by twisted
That's exactly what I needed to know.

Also right now I can only select a city from lstDet or lstDep. I want to select a city from each one. Do you know why this is happening? They are two different ListView boxes so I should be able to select an item for each one right.

You will have to post your selection code. You could be using the same variable for both or you may not be correctly using the SelectedIndexChanged event of the listviews properly.

Your reference to the array should be something like:

dblMileage(lstdep.ListView1.SelectedIndices(0),  _
lstdet.ListView1.SelectedIndices(0))

[twisted]

I don't have any selection code yet! I just created two ListView boxes and added the Cities to their collection.

[twisted]

Private Cities(2) As String
    Private Sub ListView1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListView1.SelectedIndexChanged
        If Me.ListView1.SelectedItems.Count > 0 Then
            Cities(0) = Me.ListView1.SelectedItems(0).Text
        End If
    End Sub
    Private Sub ListView2_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListView2.SelectedIndexChanged
        If Me.ListView1.SelectedItems.Count > 0 Then
            Cities(1) = Me.ListView2.SelectedItems(0).Text
        End If
    End Sub
If Cities(0).Length = 0 Then
    MessageBox.Show("You need to select a Destination City", "Error")
    ElseIf Cities(1).Length = 0 Then
    MessageBox.Show("You need to select a Departure City", "Error")
    End If

LIKE THIS???

[CyberHawke]

Yep, that's the correct way to do what you are trying to accomplish.

[taxes]

Hi,

O.K. Let us see your code for adding the cities to the listviews.

[twisted]

I don't have code for adding the cities to the ListView. I just went into ListView properties and added them through Collection. Is this right??

[taxes]

Originally posted by twisted
I don't have code for adding the cities to the ListView. I just went into ListView properties and added them through Collection. Is this right??

Sure, that's OK.

So, are you still having problems selecting a city from each listview?

[twisted]

Private Sub mnuMileage_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles mnuMileage.Click
        '                   Boston   Chicago    Dallas  Las Vegas   Los Angeles Miami   Washington D.C  
        ' Boston            0        1004       1753    2752        3017        1520    448
        ' Chicago           1004     0          921     1780        2048        1397    709
        ' Dallas            1753     921        0       1230        1399        1343    1307
        ' Las Vegas         2752     1780       1230    0           272         2570    2420
        ' Los Angeles       3017     2048       1399    272         0           2716    2646
        ' Miami             1520     1397       1343    2570        2716        0       1057
        ' Washington D.C.   448      709        1307    2420        2646        1057    0
        
        Dim dblMileage(6, 6) As Double
        dblMileage(0, 0) = 0
        dblMileage(0, 1) = 1004
        dblMileage(0, 2) = 1753
        dblMileage(0, 3) = 2752
        dblMileage(0, 4) = 3017
        dblMileage(0, 5) = 1520
        dblMileage(0, 6) = 448
        dblMileage(1, 0) = 1004
        dblMileage(1, 1) = 0
        dblMileage(1, 2) = 921
        dblMileage(1, 3) = 1780
        dblMileage(1, 4) = 2048
        dblMileage(1, 5) = 1397
        dblMileage(1, 6) = 709
        dblMileage(2, 0) = 1753
        dblMileage(2, 1) = 921
        dblMileage(2, 2) = 0
        dblMileage(2, 3) = 1230
        dblMileage(2, 4) = 1399
        dblMileage(2, 5) = 1343
        dblMileage(2, 6) = 1307
        dblMileage(3, 0) = 2752
        dblMileage(3, 1) = 1780
        dblMileage(3, 2) = 1230
        dblMileage(3, 3) = 0
        dblMileage(3, 4) = 272
        dblMileage(3, 5) = 2570
        dblMileage(3, 6) = 2420
        dblMileage(4, 0) = 3017
        dblMileage(4, 1) = 2048
        dblMileage(4, 2) = 1399
        dblMileage(4, 3) = 272
        dblMileage(4, 4) = 0
        dblMileage(4, 5) = 2716
        dblMileage(4, 6) = 2646
        dblMileage(5, 0) = 1520
        dblMileage(5, 1) = 1397
        dblMileage(5, 2) = 1343
        dblMileage(5, 3) = 2570
        dblMileage(5, 4) = 2716
        dblMileage(5, 5) = 0
        dblMileage(5, 6) = 1057
        dblMileage(6, 0) = 448
        dblMileage(6, 1) = 709
        dblMileage(6, 2) = 1307
        dblMileage(6, 3) = 2420
        dblMileage(6, 4) = 2646
        dblMileage(6, 5) = 1057
        dblMileage(6, 6) = 0
 
If Cities(0).Length = 0 Then
    MessageBox.Show("You need to select a Destination City", "Error")
    ElseIf Cities(1).Length = 0 Then
    MessageBox.Show("You need to select a Departure City", "Error")
    End If
    End Sub
Private Cities(2) As String
    Private Sub lstDep_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lstDep.SelectedIndexChanged
        If Me.lstDep.SelectedItems.Count > 0 Then
            Cities(0) = Me.lstDep.SelectedItems(0).Text
        End If
    End Sub
    Private Sub lstDet_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lstDet.SelectedIndexChanged
        If Me.lstDet.SelectedItems.Count > 0 Then
            Cities(1) = Me.lstDet.SelectedItems(0).Text
        End If
    End Sub

This is what I have set up! And yes, still problems I can only select one from either.

[taxes]

Hi,

Your immediate problem is that

If Cities(0).Length = 0 Then
MessageBox.Show("You need to select a Destination City", "Error")
ElseIf Cities(1).Length = 0 Then
MessageBox.Show("You need to select a Departure City", "Error")
End If

Is not included in any sub. Presumeably you intemded it to be inserted in the mnuMileage_Click event.

I do not undetstand why you are not getting an error message during your coding.

[twisted]

I did edit my code to reflect that before you posted but am still getting this error:

An unhandled exception of type 'System.NullReferenceException' occurred in Mileage Lookup.exe

Additional information: Object reference not set to an instance of an object.

If Cities(0).Length = 0 And Cities(1).Length = 0 Then
            MessageBox.Show("You need to select a Departure and Destination City", "Error")
        ElseIf Cities(0).Length = 0 Then
            MessageBox.Show("You need to select a Departure City", "Error")
        ElseIf Cities(1).Length = 0 Then
            MessageBox.Show("You need to select a Destination City", "Error")
        End If

[twisted]

Maybe this will help!

SEE ALL MY CODE HERE

OK here is what I need:

1) Need to be able to select a city from each ListView

2) Need to click on View Mileage and it will pull the information from the 2D array.

These are the two things I am stuck on!

[taxes]

Hi,

Let's take this in stages.

1. Your present code DOES allow you to select one city from each listview and stores them in Cities(0) and Cities(1). What it does not do is leave both the selectied cities marked in the listviews.

2. Your error arises when one or both city selections are omitted and you have a nul value in Cities().To allow for this your validation code should be;

[Highlight=VB]
Dim strError As String =""
If Cities(0)="" and Cities(1)="" then
strError=" Departure & Destination Cities""
ElseIf Cities(0) = "" Then
strError=" a Departure City"
ElseIf Cities(1 = "" Then
strError=" a Destination City"
End If
If strError<>"" then
MesssageBox.Show("You need to enter " & strError, "Error")
[/vbpode]


3. To view the mileage just put the desired array value in a Label. Your array reference will be the index numbers of the selecteditem in lstdep and the selecteditem in lstDet (in that order)

[twisted]

dblMileage(lstDep.SelectedItems(0), lstDet.SelectedItems(0))

I did this and thought it would work but it doesn't!

Also my Message statment only works the first time. After you select one the count must be greater then 0, I guess. So it only works the first time.

[twisted]

I still can't figure it out! I'm trying to write code so it will pull the information from a 2D array of each ListView box index selection.

Say Boston to Dallas, then the user click View--> Mileage and I want it to display the information in a message box. Like this:

The total mileage between your selections is: 1753 Miles

[twisted]

This isn't right is it? It doesn't pull the values from the 2D array, will it??

Dim strMileage As String
        strMileage = "lstDep, lstDet"
        If Me.lstDep.SelectedItems.Count < 0 And Me.lstDet.SelectedItems.Count < 0 Then
            MessageBox.Show("The total miles from Departure City to Destination City is" & strMileage, "Total Mileage")
        End If

[twisted]

Originally posted by taxes
Hi,

Let's take this in stages.

1. Your present code DOES allow you to select one city from each listview and stores them in Cities(0) and Cities(1). What it does not do is leave both the selectied cities marked in the listviews.

2. Your error arises when one or both city selections are omitted and you have a nul value in Cities().To allow for this your validation code should be;

[Highlight=VB]
Dim strError As String =""
If Cities(0)="" and Cities(1)="" then
strError=" Departure & Destination Cities""
ElseIf Cities(0) = "" Then
strError=" a Departure City"
ElseIf Cities(1 = "" Then
strError=" a Destination City"
End If
If strError<>"" then
MesssageBox.Show("You need to enter " & strError, "Error")
[/vbpode]


3. To view the mileage just put the desired array value in a Label. Your array reference will be the index numbers of the selecteditem in lstdep and the selecteditem in lstDet (in that order)

So can you help me with the first one so I can try and do the rest by myself. I can't figure out if my code works without being able to select one item from each ListView. My listviews are named lstDep and lstDet and they both contain the same cities in the same order. Here is what it should look like when it's complete!

[taxes]

Originally posted by twisted
This isn't right is it? It doesn't pull the values from the 2D array, will it??

Dim strMileage As String
        strMileage = "lstDep, lstDet"
        If Me.lstDep.SelectedItems.Count < 0 And Me.lstDet.SelectedItems.Count < 0 Then
            MessageBox.Show("The total miles from Departure City to Destination City is" & strMileage, "Total Mileage")
        End If

Sorry, I've been playing tennis for the past 7 hours.

I am not over familiar with ListViews in this context as I prefer to us DropDownCombo's. This has the advantage of leaving the selected item visible in the combo window. However I am looking it all up.


What we need to find out is:

1. How can we leave the selected item of BOTH listviews
highlighted.?

2. How can we get the index number of the selecteditem of a
listview?

If anyone out there can help it would be appreciated.

Meanwhile, I will keep looking.


As the subject of this thread has completely changed now, I have started a new thread entitled ListViews.

[taxes]

Hi,

Did you see the quick response to the new thread?


What you have to do is to change the HideSelection property of the two ListViews to False.


Then something like

TextBoxMileage=dblMileage(lstDep.SelectedItems(0).Index, lstDet.SelectedItems(0).Index)

(With acknowledgments to crptcblade)

[twisted]

OK! Only thing I need to figure out still is how to retrieve data from my 2D array. This is what I want to happen but don't know how to put it into code:

I want to display a message box saying " The mileage between the cities selected is {value from 2D array}"

So I'm thinking I need to make this a string:

dblMileage(lstDep.SelectedItems(0).Index, lstDet.SelectedItems(0).Index)

So when I make it a string:


If you have selected a item from lstDep and lstDet, then MessageBox.Show("The mileage between the cities selected is" & strValue, "Mileage")

Am I hot or very cold?? And if so could someone show me how to make my string with my statement?

[techgnome]

strValue = dblMileage(lstDep.SelectedItems(0).Index, lstDet.SelectedItems(0).Index).ToString

I *think* that will do it.

TG

[twisted]

Pulls the information perfectly. Thanks!

strValue = dblMileage(lstDep.SelectedItems(0).Index, lstDet.SelectedItems(0).Index).ToString
        MessageBox.Show("The mileage between the two cities is " & strValue, "Mileage")