Why are array formulas so powerful?
They allow you to do things not possible with regular formulas, an array formula can do multiple calculations on several values simultaneously. You can do seriously complicated calculations, Excel is definitively a powerful tool.

How do I start?
Constructing an array in excel is easy. Double click on cell A1 and type ={1,2,3} in the formula bar and hold and press CTRL + SHIFT simultaneously, then press Enter once. Release all keys.

The formula must have a beginning and ending curly bracket. Don't enter those characters yourself. Make sure the formula bar looks like this: {={1,2,3}}

If your formula bar looks like the picture above then you have made your first array!

Why is only one value shown? I have 3 values in the array? There can only be one value in each cell. To be able to see all values enter the formula in cell range A1:C1

1. Select cell range A1:C1
2. Click in formula bar
3. Press and hold CTRL + SHIFT simultaneously
4. Press Enter
5. Release all keys

The animated picture above shows you how to extend an array formula from cell A1 to A1:C1, this allows you to see all values in the array.

You have now extended the formula to three cells and all values in the array are visible on the sheet, see picture above.

Arranging constants in a formula

You can construct arrays with a comma delimiter and a semicolon delimiter.

What is the difference? Use the comma when you want values horizontally and semicolon vertically. Look at the formula bar in this animated picture:

You can also combine colons and semicolons. ={1,2;3,4} A comma tells excel that the next value is to the right of the first value. A semicolon puts the next value on the next row.

I try to enter an array with text values but it doesn't work, why? Use double quotes around your values, like this: ={"A","B"}

Cell references in formulas

All arrays presented above contains constants, meaning they don´t change unless you edit them. This formula =A1:A10 contains a cell reference to A1:A10. The values in this formula change if you change a value in cell range A1:A10. Formula =A1:A10 does not contain any constants.

This means that you can use values on your sheet in your array formula. This is extremely useful.

Quickly build an array

I want to construct an array from 1 to 1000? I don´t want to enter all these values. You don't have to, the ROW function can do that for you. =ROW(1:1000) creates an array from 1 to 1000.

Hard code values

Can I hard code values from 1 to 1000 in a formula without entering them myself? Yes, you can. Type =ROW(1:1000) in the formula bar and press F9.

Excel converts =ROW(1:1000) to ={1,2,3, ... , 1000)

Is Ctrl + Shift + Enter always necessary?

Can I build an array formula without entering it as an array formula?
Yes, you often can. However it makes the formula more complicated. Read this post:  No more array formulas?

Can I enter an array formula in merged cells?

Excel tells me "Array formulas are not valid in merged cells", how can I
You can enter array formulas in merged cells: How to enter array formulas in merged cells

Are there any exceptions?

Yes, both the SUMPRODUCT function and the LOOKUP function lets you build arrays without requiring you to enter it as an array formula.

How to use the SUMPRODUCT function

How to use the LOOKUP function

The INDEX function lets you encapsulate an array so you don't need to enter it as an array formula:

Convert array formula to a regular formula

How to use the INDEX function

Any caveats?

A major disadvantage with array formulas is that if you double click on a cell containing an array formula and then clicks on another cell, the array formula changes to a regular formula. Beginner Excel users may not know about this and could possibly break your worksheet calculations.

However, this is not the case if you press Escape key to exit editing an array formula or if you press CTRL + SHIFT + Enter.

Array formulas can slow down your worksheet calculations.

 

Alright, show me some useful array formulas? 

5 easy ways to extract Unique Distinct Values

5 easy ways to VLOOKUP and return multiple values

Repeat values across cells

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