Replacing a char in a string based on a condition [duplicate] - swift

Question

This question already has answers here:
Any way to replace characters on Swift String?
(23 answers)
Closed 8 months ago.
I came across this question in CodeWars recently & tried to solve it using Swift 5 (which I'm new to):
Given a string of digits, you should replace any digit below 5 with '0' and any digit 5 and above with '1'. Return the resulting string.
Note: input will never be an empty string
I come from a Python background where we could using indexing with if statements to solve this particular problem like this:
def bin(x):
newstr = ""
for num in x:
if int(num) < 5:
newstr += "0"
else:
newstr += "1"
return newstr
But when I tried to use indexing in Swift( like the Python style), I failed...which, after a while of researching made me come across this method: String.replacingOccurrences(of: , with: )
So if my Swift code for the above ques is like this:
func fakeBin(digits: String) -> String {
for i in digits{
if (Int(i)<5){
some code to replace the char with '0'
}
else{some code to replace the char with '1'}
return digits
}
How do I use the above method String.replacingOccurrences(of: , with: ) in my code and achieve the desired output? If this is not possible, how else can we do it?
Note: I have already looked up for solutions on the website & found one:How do I check each individual digit within a string? But wasn't of any use to me as the questioner wanted the help in Java

Answer 1

A Swift String is a collection of Characters. You can map each character to "0" or "1", and join the result to a new string:
func fakeBin(digits: String) -> String {
return String(digits.map { $0 < "5" ? "0" : "1" })
}

Answer 2

Your code equivalent would be:
func fakeBinBasicForLoop(digits: String) -> String {
var output = ""
for aChar in digits {
if let intValue = Int(String(aChar)) { //It's a number
if intValue < 5 {
output.append("0")
} else {
output.append("1")
}
} else { //Not a number
output.append(aChar)
}
}
return output
}
I'm checking if it's an integer, just in case.
Manually, with replacingOccurrences(of:with:):
func fakeBinReplacingOccurences(digits: String) -> String {
var output = digits
output = output.replacingOccurrences(of: "0", with: "0") //No really needed in this case, we can ommit it
output = output.replacingOccurrences(of: "1", with: "0")
output = output.replacingOccurrences(of: "2", with: "0")
output = output.replacingOccurrences(of: "3", with: "0")
output = output.replacingOccurrences(of: "4", with: "0")
output = output.replacingOccurrences(of: "5", with: "1")
output = output.replacingOccurrences(of: "6", with: "1")
output = output.replacingOccurrences(of: "7", with: "1")
output = output.replacingOccurrences(of: "8", with: "1")
output = output.replacingOccurrences(of: "9", with: "1")
return output
}
The issue is that it iterate all the string each time, so you'll have 9 loops.
Allso, if you start by replacing 5, 6, 7, 8, 9 (ie in reverse order), your higher values will be replaced by 1, and then, replaced by 0. Order matters.
An alternative solution with reduce(into:_:):
func fakeBinReduceInto(digits: String) -> String {
let output = digits.reduce(into: "") { partialResult, character in
guard let intValue = Int(String(character)) else { partialResult.append(character); return }
if intValue < 5 {
partialResult.append("0")
} else {
partialResult.append("1")
}
}
return output
}
You can also use a map() as suggested by other answers.