Module 3 - Applied UDFs - 1

Transcription

1 Module 3 - Applied UDFs TOPICS COVERED: This module will continue the discussion of the UDF JOIN covered in the previous video... 1) Testing a Variant for Its Type (0:05) 2) Force the Creation of an Array from a Range (1:15) 3) Using Conditions for the Input Parameter (3:07) 4) Error Handling (8:35) 5) UDF's Are Versatile! (10:25) 6) UDFs as a Source for Charting (14:18) 7) Forecasting Sales (16:50) 8) Create Our Own UDF to Calculate the Trend Cycle (19:00) 9) Charting the Sales Data (22:00) 10) Plotting the Trend Cycle (24:25) 11) Benefits of Charting with UDFs (25:30) Testing a Variant for Its Type (0:05) Using the Immediate Window, the variant va can be tested to find out its variable type. (1) Use the.address property. The result returned is a range. (2) Use the UBound function. Since va is being passed to the UDF as a range, the UBound function Module 3 - Applied UDFs - 1

2 throws an error. (3) Use the TypeOf function. The conditional statement returns a true value. Even if the UDF is array-entered (Ctrl-Shift-Enter), the variant is still not passed an array. Force the Creation of an Array from a Range (1:15) The combination of array-entering and boolean evaluation of a range forces Excel to produce an array of boolean results. Applying this method to the UDF JOIN indeed passes an array to the UDF. And an interesting result appears when applying this method to the UDF. A concatenated string of FALSE and TRUE values for each cell of the range, s, where the condition of equalling "x" is true. Using Conditions for the Input Parameter (3:07) The UDF can be fed a variety of conditions that will result in a boolean evaluation. Module 3 - Applied UDFs - 2

3 Introducing OR logic as an Input Parameter All of these examples produce an array for the input parameter to JOIN that is 1 column wide by 13 rows tall (1 x 13), the same as the range s. NOTE: The array is processed within the UDF by columns first. However, if we incorporate OR logic into the boolean tests, the array input parameter to JOIN will be as wide as however many alternatives are compared. The example formula above creates an array of 3 columns wide and 13 rows tall. Module 3 - Applied UDFs - 3

4 Sorting Concatenated Values Alphabetically The column function returns a horizontal vector array from 97 to 122 which are the character codes from A - Z. Error Handling (8:35) Module 3 - Applied UDFs - 4

5 VBA routines should always include error handling code. This is especially important for UDFs. And fortunately, it is very easy to add. (1) Near the top of the routine, add the On Error statement. If an error occurs while executing the routine, it will send the routine to the ErrorHandler code section. (2) At the end of the routine, add the ErrorHandler code. Add the actual error handling code in this section. (3) Before the ErrorHandler section, add an Exit Function statement. This will allow VBA to exit the function without executing the ErrorHandler code if no error occurs. (4) The error handling code can be as simple or complex as you wish. In this example, the code simply sets the function JOIN equal to the actual value of the error. UDF's Are Versatile! (10:25) Module 3 - Applied UDFs - 5

6 UDFs are NOT slow. As discussed in previous modules, it is passing through the boundary between VBA and Excel that is slow. UDFs can return more than just a single value to the caller. UDFs can return an array to the caller. MyUDF above demonstrates the return of a 100 x 1 array. And it is very fast, returning all elements to the worksheet very efficiently in one instant. UDFs as a Source for Charting (14:18) Module 3 - Applied UDFs - 6

7 Since the UDF returns an array, can it be used as the source for a chart? The answer is no. However, it can be referenced in a named formula, and the named formula can be used as the source in a chart. So it is an easy workaround. NOTE: Make sure to include the parentheses in the UDF reference or the named formula will return an error. Performance Impact of Named Formulas Referencing UDFs Named formulas are not evaluated when they are entered in the Name Manger. If no part of the workbook references the named formula, there is no performance impact on the worksheet. Charting the UDF Add the named formula as the source of the chart, and voilà, the UDF is successfully plotted in a chart! 100 data points, fast and efficient. Module 3 - Applied UDFs - 7

8 Forecasting Sales (16:50) Trend Cycle is computed with the center moving average which is a bit different when the number of periods is even. Center Moving Average: The average of two moving averages offset by one period. There is nothing wrong with using this technique. But this is a calculation intensive way to do it. A faster way would be to create a user-defined function. Module 3 - Applied UDFs - 8

9 Create Our Own UDF to Calculate the Trend Cycle (19:00) Forcing any ranges that are input through the va paramater to be turned into an array since arrays are faster to work with. And we also use the.value2 property of the range va which is about 20% faster than.value. A much better alternative when working with large amounts of data. The details of the code are not discussed in this module. Module 3 - Applied UDFs - 9

10 Testing the UDF After creating named ranges for sales (for the range B3:B42) and for periods (4 periods in each average), the UDF is array entered using the named ranges. And the output is exactly the same as the traditional calculated way of doing it! Module 3 - Applied UDFs - 10

11 Charting the Sales Data (22:00) Set the Series Y values equal to the named range sales. Remember to specify the sheet name (Sheet3!sales). Module 3 - Applied UDFs - 11

12 Create Named Range for Sales Periods incr will be used as an increment through each sales period. There are 40 sales periods plotted. Create Named Range for Trend Cycle Periods The trend cycle periods are offset from sales by two. So create a second incrementing named range, Module 3 - Applied UDFs - 12

13 incr_tc, to represent the trend cycle periods. Create Named Range for Trend Cycle The named range, tc, utilizes the UDF cma() with the parameters sales and periods. Plotting the Trend Cycle (24:25) Module 3 - Applied UDFs - 13

14 Plotting the Trend Cycle Notice the trend cycle is offset from the sales data by two periods. Benefits of Charting with UDFs (25:30) As the number of periods increase, this UDF approach to charting data can be significantly faster versus using all of the sheet calculations to achieve the same. Using arrays can dramatically increase the speed of a model. And it also makes for a very clean presentation. Module 3 - Applied UDFs - 14