What does the LET function do in a spreadsheet?
LET gives names to values inside one formula, so each is worked out once and the formula reads clearly. Here is how it works in Grid by Zaweba.
LET lets you give a name to a value or calculation inside a single formula, then use that name in the rest of the formula. The named part is calculated once, however many times you use it, and the formula becomes far easier to read. Grid by Zaweba supports LET in full, alongside LAMBDA for building your own functions.
The problem it solves
Long formulas often repeat themselves. Picture a formula that looks up a customer's total, then checks whether that total is over a limit, then applies a discount to the same total. The lookup appears three times. That makes the formula long, means the spreadsheet works out the same lookup three times, and gives you three places to fix if the lookup ever changes.
LET removes the repetition. You name the lookup once, say total, and the rest of the formula simply says total wherever it needs it.
How it's written
LET takes pairs of a name and a value, followed by a final calculation that uses the names. So a formula might name total as the result of a lookup, name rate as a discount from a cell, and then return total multiplied by one minus rate when total is over a limit. Each name can use the ones before it, so you can build up a calculation in steps, the way you'd work it out on paper.
Names inside a LET belong only to that formula. They don't clash with workbook names from Name Manager, and they don't appear anywhere else.
Where it helps most
Formulas with a repeated lookup or a repeated FILTER are the obvious candidates. Wrapping the repeated part in LET makes the formula shorter and saves Grid working the same thing out again.
Dynamic array formulas benefit too. A formula that filters a table, sorts it and then takes the top few rows reads much better when each step has a name: filtered, sorted, top. Anyone opening the sheet later can follow the logic without untangling nested brackets.
Checking your work is easier as well. While building a LET, you can make the final calculation return one of the intermediate names to see what it holds, then switch it back when you're sure.
LET and LAMBDA together
LET names values inside one formula. LAMBDA goes further and turns a formula into a function of your own, which you can save under a name in Name Manager and use across the workbook. The two work well together: a LAMBDA's body is often a LET that names the steps of the calculation. Grid supports named LAMBDAs, recursion, optional parameters and the helper functions MAP, REDUCE, SCAN, BYROW, BYCOL and MAKEARRAY.
Typing LET in Grid
Start typing =LET and autocomplete offers it, with a tip showing which argument you're on in bold. For a long LET, Alt+Enter adds a new line inside the cell, so each name can sit on its own line in the formula bar, and the formula bar can be expanded to show it all. Grid's colour-coded reference boxes show which cells each part refers to as you edit.
A few habits
Choose short, plain names that say what the value is. Avoid names that look like cell addresses, such as AB1, since those would be confusing to read.
Don't feel every formula needs LET. A short formula that uses a value once is clearer without it. LET earns its place when a formula repeats itself or has several steps.
LET is one of the quieter additions to modern spreadsheets, but it changes how readable your work is. In Grid by Zaweba it's ready to use in any formula, free and offline.
