# subscript(_:) Accesses the multiarray by using a number array that has an element for each dimension. ``` subscript(key: [NSNumber]) -> NSNumber { get set } ``` ## Parameters `key` An array that represents a position in a multiarray in which each element is an index in the corresponding dimension. ## Return Value A number. ## Discussion Use this subscript to access the multiarray by using an array in which each element is an index in the multiarray’s corresponding dimension. ```swift // 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 `MLMultiArray/strides`). ```swift // Get a pointer to the multiarray’s contents. let pointer = UnsafeMutablePointer(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 ``` --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)