Having trouble assigning a new variant array from another array - arrays

Question

I'm trying to read a range that has data as:
date&time price1 price2 price3 price4
and lots of rows going back many months/years (multiple entries per day). In the first instance, I'm trying to read this as a range from the spreadsheet, load it into a variant array and then cycle through the array only picking the data for a particular day. Once I have that (I call it today_data) I'll then do more calculations on it. Right now, I have defined the new array (today_data as variant), and Excel VBA is not allowing me to assign a value to it from the bigger array. I'm new to this please tell me what I'm doing wrong? Here is the code:
Function test1(td As Long) As Variant
Dim rg As Range
Dim n, m As Long
Dim i, j, k As Long
'intra day data is an n by m array
'i and j are counters for the loops
'td is today's date from the spreadsheet
Dim iday_data As Variant ' this is the full array of intra-day data
Dim today_data As Variant ' this is today's intra-day data
Set rg = ThisWorkbook.Worksheets("Sheet1").Range("i7:m3201")
iday_data = rg
n = UBound(iday_data, 1)
m = UBound(iday_data, 2)
k = 1
For i = 1 To n
today_data(k, 1) = iday_data(i, 1) 'this is where the program halts
today_data(k, 2) = iday_data(i, 2)
today_data(k, 3) = iday_data(i, 3)
today_data(k, 4) = iday_data(i, 4)
k = k + 1
Next i
test1 = today_data

Answer 1

Here is an example using ReDim Preserve.
I have assumed the date is formatted as a date and is in column I and that you want to compare this against long passed into function as td argument. So I have added in a test line for qualifying rows with: If DateValue(iday_data(1, jColumn)) = td Then
As you only work with 4 columns, I restrict range read in to end at L.
I first swop rows and columns as you can only redim the outer dimension. You will be wanting the matching row count for column 1 so I switched these around with Transpose and later swop them back again after the ReDim Preserve at the end. There are some limitations to row oount with Transpose.
43267 was "16/06/2018", format "dd-mm-yyyy", passed in as a numeric value i.e. td argument for date comparison which expects a Long.
Code:
Option Explicit
Public Sub Testing()
Dim arr()
arr = test1(43267)
Stop
End Sub
Public Function test1(ByVal td As Long) As Variant
Dim targetRange As Range, numberOfRows As Long, numberOfColumns As Long
Dim iRow As Long, jColumn As Long, columnCounter As Long
Dim iday_data(), today_data()
Set targetRange = ThisWorkbook.Worksheets("Sheet1").Range("I7:L3201") 'Assume L not M as you only work with 4 columns.
iday_data = targetRange
iday_data = Application.WorksheetFunction.Transpose(iday_data) 'swop rows and columns
numberOfRows = UBound(iday_data, 1)
numberOfColumns = UBound(iday_data, 2)
ReDim today_data(1 To numberOfRows, 1 To numberOfColumns)
For iRow = LBound(iday_data, 1) To UBound(iday_data, 1) 'loop between Bounds
columnCounter = 1
For jColumn = LBound(iday_data, 2) To UBound(iday_data, 2)
'Note date value assume Date format in sheet and you want to compare against long passed into function as td argument
'<== Add in your date/day of interest. Compare against which ever column of iday_data has the day of interest in e.g. 1.
If DateValue(iday_data(1, jColumn)) = td Then
today_data(iRow, columnCounter) = iday_data(iRow, jColumn)
columnCounter = columnCounter + 1
End If
Next
Next
ReDim Preserve today_data(1 To numberOfRows, 1 To columnCounter)
today_data = Application.WorksheetFunction.Transpose(today_data) 'swop rows and columns
test1 = today_data
End Function