B4J Library [B4X][ListOfArrays] wLOAExtras.b4xlib for Evaluating Expressions of Columns in ListOfArrays - and More

William Lancee · Mar 31, 2026

Version 1.01 updated in #1

After continued testing - corrected some bugs.

William Lancee · Mar 31, 2026

Here is a B4Xpages project with many examples of using the wLOAExtras library.
Make sure to add the library (see #1) to your Additional folder.

William Lancee · Mar 31, 2026

Some comments about DateTime methods in wLOAExtras.

The first group of methods convert date strings to DateTime Longs: ToDate ToTime ToDateTime
Strings must be in the DateTime.DateFormat set prior to use of these methods.
For ToDateTime, strings must be in [DateFormat]_T_[TimeFormat]. Ex. "1 JAN 2026_T_12:30"

These methods return Date Longs corresponding to Date Strings in the column spec.
"colspec" can be: 1. column names as List; 2. column names as Array; 3. column name as String
If colspec is Null or Array() or "" the operations will be applied to all columns
The original is un-affected. The result has the same number of rows as the original LOA.

If the date/time string is invalid (does not conform to the specified DateTime formats) the result will be Null.

Date Longs can also be created by specifying Years, Months, Days, Hours, Minutes, Seconds; if a value is omitted it is set to 0.
DateAndTime(LOA As ListOfArrays, colspec As Object, params() As Object) As ListOfArrays

The following methods take Data Longs in columns into date strings in a new LOA:
AsDate AsTime AsDateTime

All the standard DateTime methods are implemented
DayOfYear DayOfMonth DayOfWeek Weekday Week Year Month MonthName Hour Minute Second

Some extra methods are:
Month3lets Month3caps Weekday3lets Weekday3caps Quarter

Three methods are taken from DateUtils:
AddPeriod DaysBetween Monthdays (For a month and year in a column of Date Longs - Feb, 2024 => 29)

Why are DataTime functions not implemented in the expressions used in EvalReplace, EvalAppend, and EvalCreate?
I always wanted to say this: "It was a design decision and functionality is not affected"

William Lancee · 2026-04-07T18:09:54+0100

Version 1.03 Post #1 is updated

1. Added features to accomodate objects in ListOfArrays that are not scalar.
2. Fine tuned error reporting - now you get the B4J source line # instead of Java line #
3. Added a statistical summary of numerical columns

Scalar types are: Int, Float, Double, Long, Byte, Short, String, Boolean, Char
The first example uses an Array to store the x and y of a Point (as you could do on a canvas or bitmap).

B4X:

    'create some random data points (x,y tuples)
    RndSeed(42)  'to keep demo testing consistent
    Dim data(6) As Object
    For i = 0 To 5
        data(i) = Array(Rnd(0, 600), Rnd(0, 600))
    Next
    Dim TuplesLOA As ListOfArrays = wLOA.collect(3, 2, data)
    wLOA.Display(TuplesLOA, 0, 0)
#If DemoLog
________ TuplesLOA __________
A                 B          
――――――――――――――――――――――――
530,363     48,284
570,325     305,518
319,293     182,302
―――――――――――― #rows=3 #cols=2
#End If

    'iterate through TuplesLOA and compute Distance between the two columns
    Dim ls As LOASet = TuplesLOA.CreateLOASet
    Dim lst As List: lst.Initialize
    Do While ls.NextRow
        Dim A() As Object = ls.GetValue("A")
        Dim B() As Object = ls.GetValue("B")
        lst.Add(Sqrt((A(0) - B(0)) * (A(0) - B(0)) + (A(1) - B(1)) * (A(1) - B(1))))
    Loop
    TuplesLOA.AddColumn("Distance", lst)
    wLOA.Display(TuplesLOA, 0, 1)
#If DemoLog
________ TuplesLOA __________
A                 B     Distance
――――――――――――――――――――――――
530,363     48,284      488.4    
570,325     305,518     327.8    
319,293     182,302     137.3    
―――――――――――― #rows=3 #cols=3
#End If

The second example uses the Point class instead of an tuples array (Point class is included in the Deomo1.03.zip)
I also tested how fast it would be on my system in release mode.
It took 243 msecs to compute distance and slope for the two columns A and B of a LOA with 1 million rows.

B4X:

    Dim n As Int = 1000000
    RndSeed(42)  'to keep demo testing consistent - i.e. same points as data above, same results
    Dim pts(n) As Point
    For i = 0 To n - 1
        pts(i) = pt.new(Rnd(0, 600), Rnd(0, 600))
    Next
 
    Dim markTime As Long = DateTime.now
    Dim PointsLOA As ListOfArrays = wLOA.collect(n, 2, pts)
    Dim lst1 As List = wLOA.emptyLst
    Dim lst2 As List = wLOA.emptyLst
    Dim ls As LOASet = PointsLOA.CreateLOASet
    Do While ls.NextRow
        Dim PA As Point = ls.GetValue("A")
        Dim PB As Point = ls.GetValue("B")
        lst1.Add(PA.distance(PB))
        lst2.Add(PA.slope(PB))
    Loop
    PointsLOA.AddColumn("Distance", lst1)
    PointsLOA.AddColumn("Slope", lst2)
    Log($"Time to do above task on 1000000 rows: ${DateTime.Now - markTime} msecs"$)
    '243 msecs on 11th Gen Intel(R) Core(TM) i9-11900K @ 3.50GH

    wLOA.Display(PointsLOA, 5, 3)

#If DemoLog
________ PointsLOA __________
A                       B      Distance       Slope        
――――――――――――――――――――――――
(530, 363)     (48, 284)      488.431         0.164        
(570, 325)     (305, 518)     327.832         -0.728      
(319, 293)     (182, 302)     137.295         -0.066      
(276, 492)     (476, 32)      501.597         -2.300      
(456, 570)     (343, 209)     378.272         3.195        
―――first 5 rows―― #rows=1000000 #cols=4

Time to do above task on 1000000 rows: 243 msecs
#End If

The next example shows a statistical summary of numerical data columns

B4X:

    Dim SampleLOA As ListOfArrays = wLOA.randomInt(100, 3, Array(1, 10))
    SampleLOA.SetValue(3, 1, Null)
    SampleLOA.SetValue(5, 2, "This is unsual")
    wLOA.display(SampleLOA, 7, -1)
#If DemoLog
________ SampleLOA __________
A             B             C                        
――――――――――――――――――――――――
2             5             5                        
3             9             10                      
6             7             9                        
8             --            7                        
1             1             5                        
7             4             This is unsual
2             1             9                        
―――first 7 rows―― #rows=100 #cols=3
#End If

    Dim StatsLOA As ListOfArrays = wLOA.StatsNumerical(SampleLOA, Array(), 5, "%")
    wLOA.display(StatsLOA, 0, -1)
#If DemoLog
________ StatsLOA __________
Statistic           A             B             C      
――――――――――――――――――――――――
Number Valid       100            99            99    
Minimum              1             1             1      
Maximum             10            10            10    
Sum                553           544           559  
Mean               5.5           5.5           5.6  
Variance          9.08          8.40          9.05
Std. Dev.         3.01          2.90          3.01
Bin Size          1.80          1.80          1.80
Bin #1             21%           20%           23%  
Bin #2             21%           20%           14%  
Bin #3             13%           17%           14%  
Bin #4             24%           25%           26%  
Bin #5             21%           17%           22%  
1%tile               1             1             1      
5%tile               1             1             1      
10%tile              1             1             1      
25%tile              2             1             1      
33.3%tile            3             3             3      
50%(Median)          3             4             4      
66.7%tile            6             6             6      
75%tile              7             7             8      
90%tile              8             8             8      
95%tile             10             9             9      
99%tile             10            10            10    
―――――――――――― #rows=24 #cols=4
#End If
    Log(wLOA.GetStdDev(StatsLOA))
#If DemoLog
{A=3.0132870739275717, B=2.8974786272520454, C=3.0078575035218136}
#End If

This example illustrates error reporting:

B4X:

    'Create a 5 x 3 table of random number with default column names
    Dim LOA4 As ListOfArrays = wLOA.randomDouble(5, 3, 5)
    wLOA.evalReplace(LOA4, Array(), "XX + 360 * ?")
#If DemoLog
ERR: Unknown item 'xx' in expression:  XX + 360 * ? [b4xmainpage line 99]
#End If

Attached are the examples as a B4XPages project, tested on B4J and B4A.
Make sure to add latest version of wLOAExtras.b4xlib (see post#1) to your Additional folder

B4J Library [B4X][ListOfArrays] wLOAExtras.b4xlib for Evaluating Expressions of Columns in ListOfArrays - and More

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William Lancee

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William Lancee

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