Anatomy of an if function

An if function is pretty simple - you write a test condition that will produce a true or false value when evaluated. If true, it will execute one set of functions that you designate, if false, another.

Or, in pseudocode:
if (<test condition>,
<execute these functions if true>,
<execute these functions if false>)

An if function is great if you want to only edit certain cells in a column, but not others. The hardest part, though, is writing the test condition. Basically, all you're really doing is trying to stack functions together to make GREL spit out a boolean. Here are a few hints to help write the test conditions.

Create custom facet names by using an if function

 I covered custom faceting using booleans in this post. The other nice feature with custom facets is that if you don't want the labels "true" and "false" for your facet, you can just drop your boolean into an if function, and you can name your own facets.

In the custom facet I created using booleans, I used this piece of GREL to facet out any 856 |3 data that started with a volume label and didn't have a semi-colon:

and(value.startsWith("v"), not(value.contains(";")))

If structure cheat sheet

Updated 8/24/17

If structure cheat sheet

<operation> can be any function – reprinting a cell value, concatenating cells values, any string processing function listed in the wiki, and even a foreach, with, or another if function.

Do <operation> only if test condition is false	if (test condition, value, <operation>)
Do <operation> only if test condition is true	if (test condition, <operation>, value)
Do <operation1> if test condition is true, otherwise do <operation 2>	if (test condition, <operation 1>, <operation 2>)
Do a Marcedit Find/Replace on string1 string2 string3 to transform it into string2; string3; string1	if (isNotNull(value.match(/(regex for string1)(regex for string2)(regex for string3)/)), value.match(/(regex for string1)(regex for string2)(regex for string3)/)[1] + “;” + value.match(/(regex for string1)(regex for string2)(regex for string3)/)[2] + “;” + value.match(/(regex for string1)(regex for string2)(regex for string3)/)[0], value)

Test Condition Cheat Sheet

Example data to be used is
auto
autos
auto mechanics
automechanics
auto mechanics and aviation
planes
trains
automobiles
aviation
aviation and automechanics

NOTE : Test conditions can also be used for custom text faceting

Test Condition	Code
String must exactly match auto	value == “auto”
String can be auto, autos, auto mechanics, automechanics, or auto mechanics and aviation	value.contains("auto")
String can be auto mechanics, automechanics, auto  mechanics, or auto mechanics and aviation.	isNotNull(value.match(/(.*auto.*mechanics.*)/))
String can be auto, autos, planes, trains, or automobiles.	isNull(value.match(/(.*auto.*mechanics.*)/))
String must match auto, autos, or planes.	or(isNotNull(value.match(/(^auto[s]/))), value == "planes")
String must start with some variation of auto.	value.startsWith("auto")
Find all of the variations of auto mechanics and aviation	and(isNotNull(value.match(/(.*auto\s*mechanics.*)/)), value.contains("aviation"))
All strings that begin with "a"	value.startsWith("a")
All strings that end with "s"	value.endsWith("s")
String must be less than 4 words	length (split(value, “ “)) < 4
String must contain any substring with variable spacing of “auto mechanics” and must be less than 4 words	and(isNotNull(value.match(/.*auto.*mechanics.*/)), length(split(value, " ")) < 4)
Cell is completely blank	isBlank(value)
Cell is not blank	isNonBlank(value)

Test conditions for dates

Test string is a single range of years, such as 1938-1968. No spaces surrounding the hyphen.

First year must be greater than 1938	toNumber(substring(value, 0,4)) > 1938
First year must equal 1938	toNumber(substring(value, 0,4)) == 1938
First year must be less than 1938	toNumber(substring(value, 0,4)) < 1938
Second year must be less than 1968	toNumber(substring(value,5,9)) < 1968
Second year must be equal 1968	toNumber(substring(value,5,9)) == 1968
Second year must be less greater than 1968	toNumber(substring(value,5,9)) > 1968
Second year is greater than the first	toNumber(substring(value,5,9)) > toNumber(substring(value,0,4))