1. 1 CS 106 Computing Fundamentals II Chapter 84 “Array Formulae” Herbert G. Mayer, PSU CS status 6/14/2013 Initial content copied verbatim from CS 106 material developed by CS professors: Cynthia Brown & Robert Martin

2. 2 Syllabus Writing Excel User Functions Writing Excel User Functions Mac vs. Windows Mac vs. Windows C C C C c

3. 3 An array formula is… An array formula is a formula that can perform multiple calculations on one or more elements of an array; it can return multiple cells instead of just one cell The multiple cells are in a rectangular shape group which could be in one row or column or in multiple rows and columns. We will call this group of cells an “array” in this context. It is not the same as a VBA array, but it is a similar concept.

4. 4 Example: Transpose We’ll illustrate the idea by creating an array formula that transposes an array There is a copy option that does the same thing, but it creates a copy that is not linked to the original, so a change in the original does not create a change in the copy This example is from “Excel, the Missing Manual” by Matthew McDonald

5. 5 Example Data This data has 15 rows and 5 columns; the values repeat down each column and increase from row to row.

6. 6 Create the Array Formula The formula is going in cells A18:E15. I typed =TRANPOSE( and selected the array of cells A1:E15. To save it as an array formula I now must type ) and then Control-Shift-Enter rather than just Enter. (Use Command-Return on a Mac)

7. 7 The Result You can see that the rows and columns have been transposed.

8. 8 I added a regular copy with transpose option These two transposed copies look the same, but they’re not

9. 9 I changed the original “array”… The copy created with the array formula changed to match the new data; the simple transposed copy did not

10. 10 Curly brackets signify an array formula Excel adds the curly brackets when you type Control-Shift-Enter (Command-Return on a Mac); they show the cell value was created using an array formula

11. 11 Changing the Formula If you want to change the formula, you need to select ALL the cells in the source array, change the formula, and then type Control-Shift-Enter (Command-Return on a Mac) to create the new formula Besides TRANSPOSE, some other functions that require array formulas are FREQUENCY and TREND

12. 12 Another Example This is taken from the article at support.microsoft.com on when to use an array formula to do a SUM with multiple IF criteria We discussed IF for worksheets early in the term; see Week 3 for details This formula also uses + as a Boolean operator: it is the same as OR

13. 13 The Data We have a company with 3 types of departments, A,B, and C Our spreadsheet has rows with department type and number of employees We want to sum the number of employees in departments of type A or B (You could also use SUMIFS, as we did in our example in Week 3)

14. 14 First Example Here we entered the following array formula in Cell D1: (curly braces added by Excel) =SUM(IF((A2:A9="A")+(A2:A9="B"),B2:B9,0)) This says that if the entry in column A is “A” or “B”, add the corresponding number in column B to the sum, else add 0. The sum of numbers with departments A or B is 16

15. 15 Second Example Note the curly braces inside this second formula! You type these explicitly; the outer ones come from using the special return combination. The formula gives the same result as the first one: =SUM(IF(A2:A9={“A”,”B”},B2:B9,0)) So in this case Excel matches any element in the inner array {“A”, “B”}

16. 16 Bottom Line There are cases where it makes sense to use these kinds of formulas Often, though, you can write a VBA program to do the same job and the program will be easier to understand and modify, and less error-prone, than the formula If you like these there is more information at http://office.microsoft.com/en-us/excel-help