Hi, How can I create this extension function sortByStringValue? I have a list that can contain strin...

# android

[Sergio C.]

Hi, How can I create this extension function sortByStringValue? I have a list that can contain strings or numbers as strings. Sorting won’t work correctly if the string contain numbers.
If I have a selector that can return String or Double it’s not accepted. Any good workaround?

val list = mutableListOf<String>("10", "0.1", "0.01", "1")
        list.sortBy { // default kotlin in-place sorter
            it
        }
        list.sortByStringValue {
            if (it.toDoubleOrNull() == null) {
                it
            } else {
                it.toDouble()
            }
        }

[Javier]

val list = listOf("10", "0.1", "0.01", "1")

list.sortByStringValue()

fun List<String>.sortByStringValue() = mapNotNull(String::toDoubleOrNull).sorted()

[Javier]

output:

[0.01, 0.1, 1.0, 10.0]

[Javier]

#codereview for the next ones, this is not related to Android 🙂

[Sergio C.]

ok thanks but that will only work for numbers

[Sergio C.]

it can have standard Strings, names, descriptions…

[Sergio C.]

I got it

[Sergio C.]

💡

[Sergio C.]

fun List<String>.sortByStringValue(): List<String> {
    if (size > 1) {
        return if (first().toDoubleOrNull() == null) {
            sortedBy { it }
        } else {
            sortedBy { it.toDoubleOrNull() }
        }
    }
    return this
}

[Javier]

why are you checking the first one

[Javier]

which can't be null, because size > 1

[Sergio C.]

yes

[Javier]

if strings and numbers are mixed, your algorithm is just thinking in the first item

[Javier]

so it will do random things

[Sergio C.]

in this case, if the first item is a number all the others will be numbers

[Sergio C.]

will be safe

[Sergio C.]

just wanted to abstract some code out of the way