how to select values from a user defined type?

Question

I've sorted my data into a user defined type where Dy is the date of the measurement, Tm is the time, and pH is the measurement.

Type pHData
    Dy As Date
    Tm As Date
    pH As Single
End Type

Now I would like to sort the data by day (each day has a different number of data points), so that I can find the mean, min, max, etc. I've already made an array of the unique dates, so now I want to select values for each unique date

Something like (sorry the syntax is not perfect, but I hope you get the idea):

For i = LBound(uniqueArr) to UBound(uniqueArr)
  For j = LBound(pHData) to UBound(pHData)
    if pHData.Dy(j)== uniqueArr(i)
       'store in temp array to find mean, etc.' 
    else
        Next i
  Next j

Any suggestions?

Answer 1

If you just want the min, max, mean, then you don't need to store the values in a temp array. See example below. Also, take care to write pHData(j).Dy, not pHData.Dy(j).

For i = LBound(uniqueArr) to UBound(uniqueArr)
  ' Re-initialise min, max, sum
  phMin = VeryLargeNumber   ' Choice of VeryLargeNumber depends on your application. 
  phMax = - VeryLargeNumber ' Make it beyond the range of possible pH values. 
  phSum = 0
  phCount = 0
  For j = LBound(pHData) to UBound(pHData)
    With phData(j)
    If .Dy== uniqueArr(i)

       ' These will be used to calculate the mean later           
       phCount = phCount + 1
       phSum = phSum + .pH  

       ' Is this the max or min so far?
       If .pH > phMax Then
         ' This is the largest pH value encountered so far
         phMax = .pH
       ElseIf .pH < phMin Then
         ' This is the smallest pH value encountered so far
         phMin = .pH
       Else
         ' This pH value is neither the largest nor smallest encountered so far.
         ' Do nothing.
       End If

    Else
       ' This measurement was not taken on this date. 
       ' Do nothing.
    End If
    End With

    phMean = phSum / phCount 

    ' Here goes some code to store this date's 
    ' min, max, and mean somewhere convenient.

  Next j
Next i

If you really want to store things in a temp array, the code will be more messy and also slower... Here we go:

Dim todaysValues() As [Whatever type you need]

For i = LBound(uniqueArr) to UBound(uniqueArr)

  ' First, count how many measurements were taken today.
  phCount = 0
  For j = LBound(pHData) to UBound(pHData)
    If phData(j).Dy== uniqueArr(i)
       phCount = phCount + 1
    Else
       ' This measurement was not taken on this date. 
       ' Do nothing.
    End If
  Next j

  ' Now resize the temp array and store today's measurements in it.
  ReDim todaysValues(1 To phCount)
  phCount = 0
  For j = LBound(pHData) to UBound(pHData)
    If phData(j).Dy== uniqueArr(i)
       phCount = phCount + 1
       todaysValues(phCount) = phData(j).pH
    Else
       ' This measurement was not taken on this date. 
       ' Do nothing.
    End If
  Next j

  ' Here goes some code to calculate statistics (min, max, etc.)

Next i

Answer 2

I was thinking I could match the Date information with an array of the unique days to sort the data by day. In this case, I don't really care about the time, I just want to use the day to group the data.

Something like:

If phData(1).Dy == Day(1)
    Then add phData(1).pH to tempArray
    'and find the mean, max, min, etc of tempArray

Answer 3

Is there any reason to store Date and Time information separately?

They're both handled as a floating point data, where the integer part represents the date whereas the decimal part, the time.

Example: 40589.5

40589 represents the day (today) 0.5 represents the time (midday)

Converting this value to date / time format, you'll have 15/Feb/2011 12:00 PM