For humans it is easy to do this, but it is hard to translate the idea of "simplified" into an algorithm.
I needed this, so I thought I'd share. Apologies if this has already done by others - if so, I couldn't find it.
P.S. It looks like I am warming up to the use of "IIF"
I needed this, so I thought I'd share. Apologies if this has already done by others - if so, I couldn't find it.
B4X:
'Mapping a range of numbers into a target number of simplified categories
Sub AppStart (Args() As String)
Dim ncategories As Int = 15 'or close to this
Dim minValue As Double = 1134.7
Dim maxValue As Double = 25185.8
Dim lowerBoundaries As List = thresholds(ncategories, minValue, maxValue)
For i = 1 To lowerBoundaries.Size - 1
Dim lower As String = NumberFormat2(lowerBoundaries.Get(i-1), 1, 5, 0, False)
Dim upper As String = NumberFormat2(lowerBoundaries.Get(i), 1, 5, 0, False)
Log(i & TAB & lower & IIf(i < lowerBoundaries.Size - 1, " up to (excl.) " & upper, " up to (incl.) " & maxValue))
Next
'Log:
'1 1000 up to (excl.) 3000
'2 3000 up to (excl.) 5000
'3 5000 up to (excl.) 7000
'4 7000 up to (excl.) 9000
'5 9000 up to (excl.) 11000
'6 11000 up to (excl.) 13000
'7 13000 up to (excl.) 15000
'8 15000 up to (excl.) 17000
'9 17000 up to (excl.) 19000
'10 19000 up to (excl.) 21000
'11 21000 up to (excl.) 23000
'12 23000 up to (excl.) 25000
'13 25000 up to (incl.) 25185.8
'This alogoritm can also be used to do the same thing for dates - with a bit of pre and post processing
DateTime.DateFormat = "yyyy-MM-dd"
Log(TAB)
Dim ncategories As Int = 15 'or close to this
Dim minDate As String = "1995-04-21"
Dim maxDate As String = "2021-07-17"
Dim lowerBoundaries As List = periods(ncategories, minDate, maxDate)
For i = 1 To lowerBoundaries.Size - 1
Dim lower As String = lowerBoundaries.Get(i-1)
Dim upper As String = lowerBoundaries.Get(i)
Log(i & TAB & lower & IIf(i < lowerBoundaries.Size - 1, " up to (excl.) " & upper, " up to (incl.) " & maxDate))
Next
'Log:
'1 1994-01-01 up to (excl.) 1996-01-01
'2 1996-01-01 up to (excl.) 1998-01-01
'3 1998-01-01 up to (excl.) 2000-01-01
'4 2000-01-01 up to (excl.) 2002-01-01
'5 2002-01-01 up to (excl.) 2004-01-01
'6 2004-01-01 up to (excl.) 2006-01-01
'7 2006-01-01 up to (excl.) 2008-01-01
'8 2008-01-01 up to (excl.) 2010-01-01
'9 2010-01-01 up to (excl.) 2012-01-01
'10 2012-01-01 up to (excl.) 2014-01-01
'11 2014-01-01 up to (excl.) 2016-01-01
'12 2016-01-01 up to (excl.) 2018-01-01
'13 2018-01-01 up to (excl.) 2020-01-01
'14 2020-01-01 up to (incl.) 2021-07-17
End Sub
B4X:
Sub thresholds(ncats As Int, minimum As Double, maximum As Double) As List
Dim result As List: result.Initialize
If ncats<>ncats Or ncats = 1/0 Or ncats = 0 Or maximum = minimum Then Return result 'Algorithm fails if ncats = (NaN or infinity or 0) Or range = 0
Dim range As Double = maximum - minimum
Dim roughStepSize As Double = range / ncats
Dim factor As Double = Power(10, Floor(Logarithm(roughStepSize, 10))) 'Factor is .001, .01, 1, 10, 100, 1000 etc.
Dim simplifiedStep As Double = factor * Ceil(roughStepSize / factor) 'need largest number, Ceil
Dim simplifiedMinimum As Double = factor * Floor(minimum / factor) 'need lowest number, Floor
Dim threshold As Double = simplifiedMinimum
Dim k As Int 'use multiplier, cumulative adding adds inaccuracy
Do Until threshold > (maximum + simplifiedStep) 'maximum should be less then largest threshold
result.add(threshold)
k = k + 1
threshold = simplifiedMinimum + k * simplifiedStep
Loop
Return result
End Sub
B4X:
Sub periods(ncats As Int, earliest As String, latest As String) As List
Dim result As List
result.Initialize
Dim dt0 As Long = DateTime.DateParse(earliest)
Dim dtn As Long = DateTime.DateParse(latest)
Dim daysBetween As Period = DateUtils.PeriodBetweenInDays(dt0, dtn)
Dim range As Long = daysBetween.Days
Dim nominalUnit As String 'determine what the units should be (days, weeks, months, years - extend for centuries etc.)
Dim minValue, maxValue As Double
minValue = dt0 / DateTime.TicksPerDay
maxValue = dtn / DateTime.TicksPerDay
If range / 365 > ncats Then
nominalUnit = "Years"
minValue = minValue / 365
maxValue = maxValue / 365
Else If range / 30 > ncats Then
nominalUnit = "Months"
minValue = minValue / 30
maxValue = maxValue / 30
Else If range / 7 > ncats Then
nominalUnit = "Weeks"
minValue = minValue / 7
maxValue = maxValue / 7
Else
nominalUnit = "Days"
End If
Dim tempResult As List = thresholds(ncats, minValue, maxValue) 'can use the numbers algorithm
For i = 0 To tempResult.Size - 1
Dim d As Long = tempResult.Get(i)
Dim dt As String
Select nominalUnit
Case "Years"
dt = DateTime.Date(d * 365 * DateTime.TicksPerDay)
dt = dt.SubString2(0, 4) & "-01-01"
Case "Months"
dt = DateTime.Date(d * 30 * DateTime.TicksPerDay)
dt = dt.SubString2(0, 7) & "-01"
Case "Weeks"
Dim ticks As Long = d * 7 * DateTime.TicksPerDay
Dim nearestSunday As Long = ticks - DateTime.GetDayOfWeek(ticks) * DateTime.TicksPerDay
dt = DateTime.Date(nearestSunday)
Case "Days"
dt = DateTime.Date(d)
End Select
result.Add(dt)
Next
Return result
End SubP.S. It looks like I am warming up to the use of "IIF"
