# compressed(using:) Returns a new data object by compressing the data object’s bytes. ``` func compressed(using algorithm: NSData.CompressionAlgorithm) throws -> Self ``` ## Parameters `algorithm` An algorithm used to compress the data. For a list of available algorithms, see [`NSData.CompressionAlgorithm`](/documentation/Foundation/NSData/CompressionAlgorithm). ## Return Value An [`NSData`](/documentation/Foundation/NSData) instance that contains the compressed buffer data. ## Discussion Use this method to compress in-memory data when you want to reduce memory usage and can afford the time to compress and decompress it. If your data object is already in a compressed format, such as media formats like JPEG images or AAC audio, additional compression may provide minimal or no reduction in memory usage. To restore this data, use [`decompressed(using:)`](/documentation/Foundation/NSData/decompressed(using:)), and specify the algorithm originally used to compress the data. The following example shows how to compress the data from a string and prints the sizes of the data instances to illustrate the amount of compression: ```swift var string = "NSData and its mutable subclass NSMutableData provide data objects, or object-oriented wrappers for byte buffers. Data objects let simple allocated buffers (that is, data with no embedded pointers) take on the behavior of Foundation objects." let data = Data(string.utf8) as NSData print ("original data size: \(data.count) bytes") do { let compressedData = try data.compressed(using: .zlib) print("zlib compressed size: \(compressedData.count) bytes") } catch { print ("Compression error: \(error)") } // Prints: // original data size: 241 bytes // zlib compressed size: 158 bytes ``` --- 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)