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CS 106Computing Fundamentals II

Chapter 84“Array Formulae”

Herbert G. Mayer, PSU CSHerbert G. Mayer, PSU CSstatus 6/14/2013status 6/14/2013

Initial content copied verbatim fromInitial content copied verbatim fromCS 106 material developed byCS 106 material developed by

CS professors: Cynthia Brown & Robert MartinCS professors: Cynthia Brown & Robert Martin

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Syllabus Writing Excel User FunctionsWriting Excel User Functions

Mac vs. WindowsMac vs. Windows

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An array formula is…

An array formula is a formula that can perform multiple An array formula is a formula that can perform multiple calculations on one or more elements of an array; it calculations on one or more elements of an array; it can return multiple cells instead of just one cellcan return multiple cells instead of just one cell

The multiple cells are in a rectangular shape group The multiple cells are in a rectangular shape group which could be in one row or column or in multiple which could be in one row or column or in multiple rows and columns. rows and columns.

We will call this group of cells an “array” in this context. 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 It is not the same as a VBA array, but it is a similar concept.concept.

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Example: Transpose

We’ll illustrate the idea by creating an array formula that We’ll illustrate the idea by creating an array formula that transposes an arraytransposes an array

There is a copy option that does the same thing, but it There is a copy option that does the same thing, but it creates a copy that is not linked to the original, so a creates a copy that is not linked to the original, so a change in the original does not create a change in the change in the original does not create a change in the copycopy

This example is from “Excel, the Missing Manual” by This example is from “Excel, the Missing Manual” by Matthew McDonaldMatthew McDonald

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Example Data

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

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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)

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The Result

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

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I added a regular copy with transpose option

These two transposed copies look the same, but they’re not

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I changed the original “array”…

The copy created with the array formulachanged to match the new data; the simple transposed copy did not

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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

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Changing the Formula

If you want to change the formula, you need to select If you want to change the formula, you need to select ALL the cells in the source array, change the formula, ALL the cells in the source array, change the formula, and then type Control-Shift-Enter (Command-Return and then type Control-Shift-Enter (Command-Return on a Mac) to create the new formula on a Mac) to create the new formula

Besides TRANSPOSE, some other functions that require Besides TRANSPOSE, some other functions that require array formulas are FREQUENCY and TRENDarray formulas are FREQUENCY and TREND

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Another Example

This is taken from the article at support.microsoft.com This is taken from the article at support.microsoft.com on when to use an array formula to do a SUM with on when to use an array formula to do a SUM with multiple IF criteriamultiple IF criteria

We discussed IF for worksheets early in the term; see We discussed IF for worksheets early in the term; see Week 3 for detailsWeek 3 for details

This formula also uses + as a Boolean operator: it is the This formula also uses + as a Boolean operator: it is the same as ORsame as OR

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The Data

We have a company with 3 types of departments, A,B, We have a company with 3 types of departments, A,B, and Cand C

Our spreadsheet has rows with department type and Our spreadsheet has rows with department type and number of employeesnumber of employees

We want to sum the number of employees in We want to sum the number of employees in departments of type A or Bdepartments of type A or B

(You could also use SUMIFS, as we did in our example (You could also use SUMIFS, as we did in our example in Week 3)in Week 3)

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First Example

Here we entered the following array formulain 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

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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”}

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Bottom Line

There are cases where it makes sense to use these There are cases where it makes sense to use these kinds of formulas kinds of formulas

Often, though, you can write a VBA program to do the Often, though, you can write a VBA program to do the same job and the program will be easier to same job and the program will be easier to understand and modify, and less error-prone, than understand and modify, and less error-prone, than the formulathe formula

If you like these there is more information at If you like these there is more information at http://office.microsoft.com/en-us/excel-helphttp://office.microsoft.com/en-us/excel-help