Extract Float from String in Swift

Question

I am able to extract numbers using below code:

let weightt = x.components(separatedBy: CharacterSet.decimalDigits.inverted).joined(separator: "")

For example, I'm getting "01" from string "0.1kg"

But how to extract "0.1" from string "0.1kg" ?

Is the number always at the start of the string or can the number be anywhere in the string? — rmaddy
– rmaddy, Commented Jul 20, 2017 at 5:57
And you should update your question with several examples of strings you need to process. Different solutions may not work for all possible input you need to handle. — rmaddy
– rmaddy, Commented Jul 20, 2017 at 6:02

Prashant Tukadiya · Accepted Answer · 2017-07-20 05:44:48Z

2

You can use

Input

 let x = "0.1kg"

let weightt = x.components(separatedBy: CharacterSet.init(charactersIn: "0123456789.").inverted).joined(separator: "")

output

0.1

answered Jul 20, 2017 at 5:44

Prashant Tukadiya

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5 Comments

Ben Lachman Over a year ago

This doesn't localize well. French for instance uses spaces and commas in formatted numbers, let alone other languages that use non-western digit characters.

Prashant Tukadiya Over a year ago

@BenLachman may be you are right but I have answered as per question asked You are free to update my answer if you have better solution I will appreciate it. Or later on I will update it as for now I am on vacation :)

Ben Lachman Over a year ago

Using Scanner is the correct solution. While this works for the single case in the original question, there are a huge number of cases where it doesn't work at all (ex. "$1.56")

Prashant Tukadiya Over a year ago

@BenLachman I have answered as per user question requirement. If you inject other scenarios that are out of the scope. so requested you to remove your downvote.

Ben Lachman Over a year ago

The point isn't to answer the exact question. The point is to give a good solution that takes into account the larger questions of good software engineering. Adding as much knowledge as possible per answer should always be the goal.

Ben Lachman · Accepted Answer · 2018-12-31 01:46:18Z

2

A good approach is to use Scanner. Example:

let string = " 0.1 kg"
let scanner = Scanner.localizedScanner(with: string)

var weight = 0.0
if scanner.scanDouble(&weight) {
    print(weight) // 0.1
}

The scanDouble()/scanFloat() methods parse all kinds of floating point notations (+12.34, -56.78, 1.23e4, 1,23, etc.), skip initial whitespace, support multiple locales, and scan as much as possible from the given string.

edited Dec 31, 2018 at 1:46

Ben Lachman

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answered Jul 20, 2017 at 7:10

Martin R

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4 Comments

Ben Lachman Over a year ago

This is the correct answer and supports correct behavior in other regions/languages.

Ilea Cristian Over a year ago

This seems very elegant. But how do you scan for the next number in a string? Can you tell the scanner to advance to the next number?

chitgoks Over a year ago

i dont get it. why is there a string variable and then a weight? i thought string would be the one that's going to be parsed. then there's a weight variable? what for

Martin R Over a year ago

@chitgoks: string is the String variable containing the string to be parsed, here " 0.1 kg". The parse result is stored in the weight variable, which has the type Double.

KKRocks · Accepted Answer · 2017-07-20 06:05:42Z

0

Try this also :

let str = "0.1kg"
let decimal = str.components(separatedBy: CharacterSet.init(charactersIn: "0123456789.").inverted).first.flatMap { Float($0) }
print(decimal ?? "")

answered Jul 20, 2017 at 6:05

KKRocks

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Comments

Saranjith · Accepted Answer · 2017-07-20 06:11:51Z

0

Use

let result = weightt.stringByReplacingOccurrencesOfString("kg", withString: "")

If you want to remove all characters from weightt use code. Means if it is gm instead of kg.

let result = string.stringByReplacingOccurrencesOfString("[^A-Za-z]", withString: "", 
options: NSStringCompareOptions.RegularExpressionSearch, range:nil).stringByTrimmingCharactersInSet(NSCharacterSet.whitespaceCharacterSet())

edited Jul 20, 2017 at 6:11

answered Jul 20, 2017 at 5:59

Saranjith

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1 Comment

rmaddy Over a year ago

Your regular expression isn't valid. Did you mean "[^A-Za-z]" to find anything that isn't a letter?

Sweeper · Accepted Answer · 2017-07-20 07:39:01Z

0

You didn't say anything about the constraints of the input, so I assume it is a valid decimal number followed by a unit.

You can use prefix to do this if that's the case:

let weight = "0.1kg"
let result = String(weight.characters.prefix {
     "012346789.".characters.contains($0)) })

edited Jul 20, 2017 at 7:39

answered Jul 20, 2017 at 6:14

Sweeper

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2 Comments

Martin R Over a year ago

Using .description for anything but debug output always feels a bit of a code smell to me (and the exact description format is not guaranteed officially). You can achieve the same with String(weight.characters.prefix { "012346789.".characters.contains($0) })

Sweeper Over a year ago

@MartinR Edited. Thank you!

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