问题描述
I found I can compare two numbers in String format directly in Swift.
Initially, I was trying to cast my String format number to double or Int, and then do the comparison. When I accidentally found I can compare them directly, I have done some tests in my playground. It seems the result are all correct, even with the numbers are empty string or "(Double)" vs "(Int)".
(Exceptions): The test cases with negative numbers in the String format will fail the comparing.
Does anyone know if this is a default behavior in Swift String? I am not sure if I can utilize this in my program.
Example:
var numStrs1 = ["15", "12.2", "15", ""]
var numStrs2 = ["13", "12", "", "23.0"]
func compareNumStr(numStr1:String, numStr2:String) -> Bool {
return numStr1 > numStr2
}
for var i = 0; i < numStrs1.count; ++i{
compareNumStr(numStrs1[i], numStrs2[i])
}
What the default implementation of string comparisons rely on is the Unicode collation algorithm source: http://oleb.net/blog/2014/07/swift-strings/
The comparison you're making right now is not a canonical Int/Double comparison, but rather how it translates to unicode. Depending on how you wish to use the information, it may not be suitable for all scenarios. Like you found out with negative numbers, you should use to .toInt method to get the number you want, and compare the integers instead of comparing the strings.
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