Android Question Hot to Redim this array?

[watesoft]

In VB:
Dim x() As Integer
Redim x(2 to 5)

In B4A:
How to do?

 

[stevel05]

I don't know VB, what does Redim x(2 to 5) do?

 

[agraham]

All arrays in B4X are indexed from zero so there is no direct equivalent.

Dim x(4)
For i = 2 To 5
    ...
    X(i-2) ...
    ...
Next

To ReDim an array just Dim it again.

 

[LucaMs]

Forget Arrays , use Lists or Maps.

Using a Map you might have:

Dim mapX As Map
mapX.Initialize
mapX.Put(2, 234)
mapX.Put(3, 3456789)

' and even:
mapX.Remove(2)

 

[watesoft]

Thanks agraham, Thanks LucaMs. I'm going to use Maps.

 

[watesoft]

Forget Arrays , use Lists or Maps.

Using a Map you might have:

Dim mapX As Map
mapX.Initialize
mapX.Put(2, 234)
mapX.Put(3, 3456789)

' and even:
mapX.Remove(2)

Hi LucaMs
This is a code used to calculate combinations of large Int numbers. It was originally written in VB6 and can run successfully. I rewrite it with B4A and replaced Array with MAP, but there are always NULL errors and run slowly. I hope to be able to run both in B4A and B4I, can you help me?

 

[LucaMs]

I found 2 problems:

1 - your change to "replace" the Mid$ function (I created a similar function and now this part does not crash);
2 - I have yet to find out why but there are problems using a Long as a Map key.
In this part of your source:

XYS.Put(i + j - 1, XYS.Get(i + j - 1) + x.Get(i) * y.Get(i))

the Map x contains: 1 (key) 1 (value).
x.Get(i) results Null only because "i" is declared as Long; if you declare it as Int, 1 is returned as expected.

Still studying

In the meantime I am attaching the B4XPages version so you can use it with B4A, B4J and B4i.

I hope to be able to run both in B4A and B4I

I am doing tests with B4J (much more direct, more comfortable debugging).

 

[stevel05]

Try explicit casting

Dim Key As Long = i + j - 1
Dim Value As Long = XYS.Get(Key) + x.Get(i) * y.Get(i)
XYS.Put(Key, Value)

 

[LucaMs]

x.Get(i)

That's the problem.
i is an Long and if you...

log(x.Get(i)) ' Null

If i was an Int...

log(x.Get(i)) ' 1 - correct.


I don't know if it would be okay for him to replace all Longs with Ints or... it is necessary to investigate the reason for this problem (this anyway!)

 

[LucaMs]

That's the problem.
i is an Long and if you...

log(x.Get(i)) ' Null

If i was an Int...

log(x.Get(i)) ' 1 - correct.


I don't know if it would be okay for him to replace all Longs with Int or... it is necessary to investigate the reason for this problem (this anyway!)

Ma per il momento... ho fame
But right now... I'm hungry
?

 

[stevel05]

x.Put(1,1)      'VB6: x(1) = 1
XYS.Put(1,1)

These lines will put the key as Int

 

[stevel05]

And this line is incorrect:

For i = 1 To x.Size + y.Size-1

Should be

For i = 1 To x.Size -1 + y.Size-1

So that plus changing the previous to:

Dim Key As Long = 1
    x.Put(Key,Key)      'VB6: x(1) = 1
    XYS.Put(Key,Key)    'VB6: XYS(1) = 1

And it completes

 

[LucaMs]

And it completes

Are you sure (now I have to digest, I cannot program ?)?

If yes, attach your version, Steve, please

 

[stevel05]

It completes, whether the result is correct is another matter

 

[LucaMs]

 

[stevel05]

As you can tell, I'm not used to B4xPages yet.

 

[watesoft]

As you can tell, I'm not used to B4xPages yet.

I found 2 problems:

1 - your change to "replace" the Mid$ function (I created a similar function and now this part does not crash);
2 - I have yet to find out why but there are problems using a Long as a Map key.
In this part of your source:

XYS.Put(i + j - 1, XYS.Get(i + j - 1) + x.Get(i) * y.Get(i))

the Map x contains: 1 (key) 1 (value).
x.Get(i) results Null only because "i" is declared as Long; if you declare it as Int, 1 is returned as expected.

Still studying

In the meantime I am attaching the B4XPages version so you can use it with B4A, B4J and B4i.

I am doing tests with B4J (much more direct, more comfortable debugging).

Thanks

I found 2 problems:

1 - your change to "replace" the Mid$ function (I created a similar function and now this part does not crash);
2 - I have yet to find out why but there are problems using a Long as a Map key.
In this part of your source:

XYS.Put(i + j - 1, XYS.Get(i + j - 1) + x.Get(i) * y.Get(i))

the Map x contains: 1 (key) 1 (value).
x.Get(i) results Null only because "i" is declared as Long; if you declare it as Int, 1 is returned as expected.

Still studying

In the meantime I am attaching the B4XPages version so you can use it with B4A, B4J and B4i.

I am doing tests with B4J (much more direct, more comfortable debugging).

Thanks LucaMs, Map may be a bit problem. I find two new methods that do not use collections. It is very fast. Although there are still limitations, it has been able to meet my needs.

One way: Formula transformation

Sub Class_Globals
    Private Root As B4XView
    Private xui As XUI
    Dim const e As Double = 2.718281828459
End Sub

Public Sub lnchoose(n As Int,m As Int) As Double
    If (m > n) Then Return 0
    If (m < n/2.0) Then m=n-m
    Dim s1 As Double
    s1=0
    Dim i As Int
    For i=m+1 To n
        Dim t1 As Double
        t1=i
        s1=s1+Logarithm(i,e)
    Next
    Dim s2 As Double
    s2=0
    Dim ub As Int
    ub = n-m
    For i=2 To ub
        s2=s2+Logarithm(i,e)
    Next
    Return s1-s2
End Sub

Public Sub Combination(n As Int,m As Int) As Double
    If (m > n) Then Return 0
    Return Power(e,lnchoose(n,m))
End Sub

Sub Button1_Click
    MsgboxAsync(Combination(1000,500),"fff")  'Result:2.702882409453408E299'
End Sub

Limitations: (1000,500) is the largest combination that can be calculated，but you can cal (2000,200); (5000,150) ......


Another way: use inline Java

Sub Process_Globals
    Private NativeMe As JavaObject
End Sub

#If JAVA
import java.math.BigDecimal;
import java.math.RoundingMode;
   
    public static BigDecimal computePaiLie(int n, int m) {
        if(m > n || n < 0 || m < 0) {
            throw new IllegalArgumentException("n must >m!");
        }
        return computerJC(n).divide(computerJC(n - m), 1, RoundingMode.HALF_UP);
    }
   
    public static BigDecimal computeZuhe(int n, int m) {
        if(m > n || n < 0 || m < 0) {
            throw new IllegalArgumentException("n must >m!");
        }
        //=n!/m!(n-m)!
       
        return computerJC(n).divide((computerJC(m).multiply(computerJC(n - m)).setScale(1, RoundingMode.HALF_UP)), 1, RoundingMode.HALF_UP);
    }
   
   
    public static BigDecimal computerJC(int n) {
        if(n < 0) {
            throw new IllegalArgumentException("n must >0!");
        } else if(n == 0) {
            return new BigDecimal(1);
        }
        BigDecimal bd = new BigDecimal(1.0);
        for(int i=n; i>=1; i--) {
            bd = bd.multiply(new BigDecimal(i)).setScale(1, RoundingMode.HALF_UP);
        }
        return bd;
    }
   
#End If

Sub Button1_Click
    Dim ZuHe As String = NativeMe.RunMethod("computeZuhe", Array(5000,2500)) 'You can cal very big num'
    MsgboxAsync(ZuHe,"fff")
End Sub

Limitations: can't use in b4i，At least i don't know how to use in b4i.

 

[watesoft]

As you can tell, I'm not used to B4xPages yet.

Thanks stevel05, your result is wrong and Not applicable to other combinations，I found two new methods,see my reply.

 

[stevel05]

Thanks stevel05, your result is wrong

No problem, I just got the code running, the result was yours. I have no idea what it is supposed to be doing