The each Keyword

The each keyword is one of the most common patterns in Power Query M, but it is also one of the most misunderstood. It is simply syntactic sugar (shorthand) for a function that takes a single parameter named _.

each Is a Function

These two expressions are identical:

each [UnitPrice] * [Quantity]

(_) => _[UnitPrice] * _[Quantity]

When you write each, the engine creates an anonymous function with one parameter called _. Inside the function body, the underscore is implicit — you can reference it directly or use bracket notation to access its fields.

Bracket Notation

Inside an each block, [ColumnName] is shorthand for _[ColumnName]. This works because _ is the current row (a record), and bracket notation accesses a field on that record.

// These are equivalent inside each:
[UnitPrice]       // bracket notation (implicit _)
_[UnitPrice]      // explicit _ reference

Common Uses

Filtering rows with Table.SelectRows:

Table.SelectRows(Sales, each [Region] = "East")

Adding calculated columns with Table.AddColumn:

Table.AddColumn(Sales, "Total", each [UnitPrice] * [Quantity], type number)

Transforming values with List.Transform:

List.Transform({1, 2, 3}, each _ * 10)
// Result: {10, 20, 30}

Note that for lists, _ is the current item (not a record), so bracket notation does not apply.

Nesting each

When you nest each expressions, each level creates its own _ scope. The inner each shadows the outer one. If you need to reference the outer scope, assign it to a named variable first:

Table.AddColumn(
    Sales,
    "Matches",
    (outerRow) =>
        Table.SelectRows(
            OtherTable,
            each [CustomerName] = outerRow[CustomerName]
        ),
    type table
)

Here, the inner each refers to rows of OtherTable, while outerRow captures the current row from Sales.

When Not to Use each

For functions that take multiple parameters, each does not apply. Use explicit parameter names instead:

List.Accumulate({1, 2, 3}, 0, (state, current) => state + current)