Hey I working in kotlin android. The string is coming from server and it might be contains digit, ch...

# android

[Vivek Modi]

Hey I working in kotlin android. The string is coming from server and it might be contains digit, character, empty string or null value. I want to convert that value in double because I want to compare value. So is there any better way to check that string only contain digit value and not empty or null in a kotlin way. The list is huge so I want a efficient way.
Price.kt

data class Price(
  var value: String? = null
)

main.kt

val defaultValue : Double = 4.23
val list = listOf(Price("2.33"), Price("fr23"), Price(""), Price(null), Price("4.23"), Price("12.23"))

list.forEach{
   if(it == defaultValue){
      println("Found It")
   }
}

[Harshit Singh]

This might work

fun String?.toProperDouble(): Double {
    return try {
        this?.toDouble() ?: (-1).toDouble()
    } catch (ex: NumberFormatException) {
        (-1).toDouble()
    }
}

[Tim Oltjenbruns]

the exception handling is probably not the most efficient way

[Tim Oltjenbruns]

@Vivek Modi do you want your invalid strings filtered out before the comparison? Or do you want your invalid strings to also be compared against valid strings?

If you want invalid strings compared to valid strings, maybe Double.NaN is an appropriate value for those invalid strings.

[Tim Oltjenbruns]

In Kotlin, comparison with a NaN is unordered. According to IEE 754
If you want them ordered, maybe choose Positive or Negative infinity, which will always be greater or less than other doubles.

Or, if you cast the doubles to Any, Kotlin changes it’s comparison to NaN being greater than Positive Infinity according to https://kotlinlang.org/docs/basic-types.html#floating-point-numbers-comparison

[Vivek Modi]

@Tim Oltjenbruns No I don't want to filter invalid string. Yes I want to compares invalid string to valid string. Do you know how can I solve this ?

[Tim Oltjenbruns]

yes, I just sent some helpful info!

[Vivek Modi]

@Tim Oltjenbruns Sorry I didn't get it. Can you please give me example?

[Tim Oltjenbruns]

if the string is null, empty, or otherwise does not parse to a double, you can return instead Double.NaN or Double.POSITIVE_INFINITY or Double.NEGATIVE_INFINITY based on how you want your invalid strings to compare

[Tim Oltjenbruns]

toDoubleOrNull() may also help

[Vivek Modi]

fun String?.toProperDouble(): Double {
         this?.toDouble() ?: Double.NaN
 }

Is this correct ?

[Tim Oltjenbruns]

toDouble will throw an exception if it is invalid

[Tim Oltjenbruns]

use toDoubleOrNull

[Tim Oltjenbruns]

Do you want to attempt to remove the leading or trailing whitespace, if present? for example do you want to consider ” 1.0" or “1.0 ” as valid?

[Tim Oltjenbruns]

You could use this?.trim()?.toDouble() in that case, but it will take more memory

[Vivek Modi]

I don't think so server wil return whitespace value

[Vivek Modi]

Thanks it really help

[Vivek Modi]

fun String?.toProperDouble(): Double {
          this?.toDoubleOrNull() ?: Double.NaN
  }