Formats bytes into a more human-readable form (e.g. MB).

formatBytes.swift

import Foundation

func format(bytes: Double) -> String {
    guard bytes > 0 else {
        return "0 bytes"
    }

    // Adapted from http://stackoverflow.com/a/18650828
    let suffixes = ["bytes", "KB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB"]
    let k: Double = 1000
    let i = floor(log(bytes) / log(k))

    // Format number with thousands separator and everything below 1 GB with no decimal places.
    let numberFormatter = NumberFormatter()
    numberFormatter.maximumFractionDigits = i < 3 ? 0 : 1
    numberFormatter.numberStyle = .decimal

    let numberString = numberFormatter.string(from: NSNumber(value: bytes / pow(k, i))) ?? "Unknown"
    let suffix = suffixes[Int(i)]
    return "\(numberString) \(suffix)"
}

Great stuff and a joy to read! Before I found this gist I was reading though the source code of ByteCountFormatter.swift which is quite massive for such a task. Your code does everything I need in about 5% of the lines of code in ByteCountFormatter.swift.

thanks for these, I took the liberty to fork them and convert them to Extensions, so I can now do nice things like

print(6969696969.stringFileSize) // 6,49 GiB

@flying-sausages: I'm glad that you found it useful. Making it into an extension is a smart idea.

let k: Double = 1000

Why k is 1000, not 1024?..

@kmi4k4k: There's some discussion of when to use 1024 vs. 1000 in the comments of the Stack Overflow answer I linked to.

It's more correct to use the "Kib", etc. abbreviations when using base 1024, because "KB", etc. actually refers to base 1000.

macOS's Get Info window, for example, reports file sizes in base 1000.