I have a list of people and each person has a TYPE. Either DIRECTOR, PROFESSOR or STUDENT. How do I...

# getting-started

[Colton Idle]

I have a list of people and each person has a TYPE. Either DIRECTOR, PROFESSOR or STUDENT.

How do I sort the list so that all students are listed after the DIRECTORS and PROFESSORS?

As a first approach to this, I think it would just be easier to just have two identical lists. filter out the students from list 1. and then filter out prof and directors from list2 and add them together.

[ephemient]

list.sortedBy { it.type == STUDENT }

since false < true

[ephemient]

although that's O(n log n) and is probably not the right solution unless you're also performing other sorting anyway

[ephemient]

if this is the only reorder that you want to do, then

val (students, others) = list.partition { it.type == STUDENT }
others + students

is more or less your approach but built into stdlib

[Colton Idle]

partition hm. Haven't heard of that.

[Colton Idle]

is partition faster than n log n

[ephemient]

O(n)

[ephemient]

in theory, if you didn't need to preserve order, you could simply swap elements in place - that's what C++'s partition function does - but Kotlin's does the obvious thing of building two new lists and filling them in order

[Colton Idle]

Interesting. Do the docs have these O(n) runtimes called out or is this just something you knonw?

[ephemient]

unlike C++, the docs to not commit to any particular complexity, no

[Colton Idle]

Cool. I'll take your word for it then. 😄

[ephemient]

or just look at the implementation, https://github.com/JetBrains/kotlin/blob/master/libraries/stdlib/common/src/generated/_Collections.kt#L3046-L3057

[ursus]

implement a normal comparator