---
title: "subscript(_:)"
framework: coreml
role: symbol
role_heading: Instance Subscript
path: "coreml/mlmultiarray/subscript(_:)-3d9el"
---

# subscript(_:)

Accesses the multiarray by using a number array that has an element for each dimension.

## Declaration

```swift
subscript(key: [NSNumber]) -> NSNumber { get set }
```

## Parameters

- `key`: An doc://com.apple.documentation/documentation/Foundation/NSNumber array that represents a position in a multiarray in which each element is an index in the corresponding dimension.

## Return Value

Return Value A number.

## Discussion

Discussion Use this subscript to access the multiarray by using an NSNumber array in which each element is an index in the multiarray’s corresponding dimension. // A multiarray with three dimensions. let multiarray = try MLMultiArray(shape: [5, 29, 17], dataType: .double)

// The subscript key with three elements. let key = [3, 5, 7] as [NSNumber]

// Set the element to π, a sentinel value. multiarray[key] = 3.141_59

// Retrieve the element as a number. let numberValue = multiarray[key] print(numberValue.doubleValue) // Prints: 3.14159 For better performance, directly access the multiarray’s underlying pointer by using a linear offset. Calculate the linear offset by summing the products of each dimension’s index with the dimension’s stride (See strides). // Get a pointer to the multiarray’s contents. let pointer = UnsafeMutablePointer<Double>(OpaquePointer(multiarray.dataPointer)) var linearOffset = 0

// Sum the products of each dimension’s number with its stride. for (dimension, stride) in zip(key, multiarray.strides) {     linearOffset += dimension.intValue * stride.intValue }

// Check that the linear offset resolves to the same element as the subscript. assert(pointer[linearOffset] == multiarray[key].doubleValue)

print(pointer[linearOffset]) // Prints: 3.14159

// Set the element to a different sentinel value. pointer[linearOffset] = 2.718_28 print(pointer[linearOffset]) // Prints: 2.71828