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`reduce(_:combine:)`

can be used in order to combine the elements of a sequence into a single value. It takes an initial value for the result, as well as a closure to apply to each element – which will return the new accumulated value.

For example, we can use it to sum an array of numbers:

```
let numbers = [2, 5, 7, 8, 10, 4]
let sum = numbers.reduce(0) {accumulator, element in
return accumulator + element
}
print(sum) // 36
```

We're passing `0`

into the initial value, as that's the logical initial value for a summation. If we passed in a value of `N`

, the resulting `sum`

would be `N + 36`

. The closure passed to `reduce`

has two arguments. `accumulator`

is the current accumulated value, which is assigned the value that the closure returns at each iteration. `element`

is the current element in the iteration.

As in this example, we're passing an `(Int, Int) -> Int`

closure to `reduce`

, which is simply outputting the addition of the two inputs – we can actually pass in the `+`

operator directly, as operators are functions in Swift:

```
let sum = numbers.reduce(0, combine: +)
```