---
title: "compress(using:)"
framework: foundation
role: symbol
role_heading: Instance Method
path: "foundation/nsmutabledata/compress(using:)"
---

# compress(using:)

Compresses the data object’s bytes using an algorithm that you specify.

## Declaration

```swift
func compress(using algorithm: NSData.CompressionAlgorithm) throws
```

## Parameters

- `algorithm`: The algorithm to use to compress the data. For a list of available algorithms, see doc://com.apple.foundation/documentation/Foundation/NSData/CompressionAlgorithm.

## Discussion

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 the data. If your data object is already in a compressed format, such as media formats like JPEG images or AAC audio, compress(using:) may provide minimal or no benefit. The following example shows how to compress data from a string and prints the sizes of the data instances to illustrate the amount of compression: 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 = NSMutableData(data: Data(string.utf8)) print ("original data size: \(data.length)") do {     try data.compress(using: .zlib)     print("zlib compressed size: \(data.length)") } catch {     print ("Compression error: \(error)") } // Prints: //  original data size: 241 //  zlib compressed size: 158

## See Also

### Compressing and Decompressing Data

- [decompress(using:)](foundation/nsmutabledata/decompress(using:).md)
- [NSData.CompressionAlgorithm](foundation/nsdata/compressionalgorithm.md)
- [NSCompressionErrorMaximum](foundation/nscompressionerrormaximum-swift.var.md)
- [NSCompressionErrorMinimum](foundation/nscompressionerrorminimum-swift.var.md)
- [NSCompressionFailedError](foundation/nscompressionfailederror-swift.var.md)
- [NSDecompressionFailedError](foundation/nsdecompressionfailederror-swift.var.md)