### Great idea and list from Todd Shackelford over at CAD Shack about formulas.....

### Revit Family Formula Examples and Tricks

__IF Statement__IF (Length < 30′, 2′ 6″, 4′)

If the Length parameter is less than 30' x = 1 , y = 22'-6"

If the Length parameter is greater than 30' this parameter will have a value of 4'-0"

__IF that Returns a String__**IF (Height > 30′, “This thing is tall”, “This thing is short”)**

If the Height parameter is greater than 30' this parameter will return

**This thing is tall**

If the Height parameter is less than 30' this parameter will return

**This thing is short**

__Nested IF Statements__IF (Length < 35’, 2′ 6″ , IF (Length < 45′, 3′ , IF (Length < 55′, 5′, 8′ ) ) )

If Length is less than 35', this parameter will have a value of 2'-6"

If Length is between 35' and 45', this parameter will have a value of 3'

If Length is between 45' and 55', this parameter will have a value of 5'

If Length is greater than 55', this parameter will have a value of 8'

__IF applied to a Yes/No condition__Length > 40'

If Length is greater than 40' the the statement is true and the Yes/No check box is checked

If Length is 40' or less the statement is false and the Yes/No check box is NOT checked

__IF OR__IF (OR (A = 1 , B = 3 ) , 10 , 5)

If A = 1 or B = 3 this parameter will have a value of 10

If A is not = 1 and B is not = 3 this parameter will have a value of 5

__IF AND__IF (AND (x = 1 , y = 2), 8 , 3 )

If x = 1 and y = 2 this parameter will have a value of 8

If x is not = 1 or y is not = 2 this parameter will have a value of 3

__Some Formula Tricks of the Trade__**This or That only with a Yes/No parameters**

By specifing that metal can not be true while Wood is true the user can only specify one of the two materials. They both can not be checked at the same time. This can be used for visibility where a left or right access panel may be required but never both.

**Pick One and Only One**

**"Don't Change Me Bro"**

**Swapping Nested Families**

In a bookcase family with a nested shelf family, follow these steps to add a parameter that will allow the user to switch from one type of shelf to another.

1. Open the original shelf family and save it as the second shelf option. Add something to make it different.

3. In the Family Types dialog create a new Type parameter named “Swappable Shelf”. Make its discipline

**Common**, its Type of Parameter and group it under

**Constraints**.

4. When you select the Type of Parameter Revit will open the Select Category dialog. Pick Generic Models.

5. Select the original shelf in the bookcase family now. In the Properties dialog, look for the Label parameter and change it to “Swappable Shelf”.

6. In the Family Types dialog Create 2 shelf types, Shelf Type 1 and Shelf Type 2. Associate the swappable shelf parameter with the appropriate type.7. Flex the family. Change the family type and verify that the shelf changes.