How to sort 'Map' values in Scala against multiple factors?

Question

I have a Map (datatype) with the following data structure:

var timePassedCamerasetB = mutable.Map.empty[String, Time];

It contains a String and a 'Time' object. The 'Time' object is made up from my own class. Below you can see what it consists of:

case class Time(daysSinceEpoch: Int, hours: Int, minutes: Int, seconds: Double)

I have saved all my data into this 'Map' variable. But there is one problem: I want to sort the values in this 'Map' variable based on multiple things, but I can't find any way to make it work.

For example. I have stored the following data within this map:

PP-33-XX -> Time(18492,3,7,0.0)
BA-12-PW -> Time(18492,9,0,40.0)
MM-11-OW -> Time(18492,3,7,16.0)
NX-66-PP -> Time(18492,3,6,30.0)
LA-53-NY -> Time(18492,9,0,56.0)

I want to sort the values in order (earliest time to latest time). This includes comparing multiple factors. First compare each daysSinceEpoch, then hours, minutes and seconds.

I want to transform the map into the following down below:

NX-66-PP -> Time(18492,3,6,30.0)
PP-33-XX -> Time(18492,3,7,0.0)
MM-11-OW -> Time(18492,3,7,16.0)
BA-12-PW -> Time(18492,9,0,40.0)
LA-53-NY -> Time(18492,9,0,56.0)

Does anyone know of an efficient way to do this? Unfortunately I can't..

Maps are unordered collections by nature, why do you care about the order? Anyways, you probably will end up using a sequence like a List and then use orderBy — Luis Miguel Mejía Suárez
– Luis Miguel Mejía Suárez, Commented Sep 10, 2021 at 19:06
Thanks for the quick reply! I do understand that. The order is very important to me for educational reasons. I get your thinking, but could you maybe explain this through code? Maybe I'll understand it better then. The end goal is to keep the sorted values in a 'Map' datatype (as pictured above) again. @LuisMiguelMejíaSuárez — Brian
– Brian, Commented Sep 10, 2021 at 19:17
I believe jwvh's answer goes in the direction you are looking for. In general, Maps don't have ordering, but specific implementations can either preserve insertion order (like ListMaps or LinkedHashMaps) or maintain ordering by key (like TreeSets). I'm not aware of Map implementations in the standard library that maintain ordering by value. — stefanobaghino
– stefanobaghino, Commented Sep 11, 2021 at 7:47
Hi @Brian, today you posted a python question on how to count the occurrence of certain climate words in a dataframe column. I was working on your question but the question got deleted. However, I found a solution that might help you. Do pattern = "|".join(list_of_words). Then use df.Clean_text.str.count(pattern). This should give you what you were looking for. — Timo
– Timo, Commented Sep 28, 2022 at 14:01

cuZzior · Accepted Answer · 2021-09-10 20:07:28Z

3

As Luis commented, Maps, specifically mutable.Map aren't designed to hold ordered values. If you could go with a List it can be easily sorted like this:

timePassedCamerasetB
    .toList
    .sortBy {
      case (_, time) => (time.daysSinceEpoch, time.hours, time.minutes, time.seconds)
    }

This expression has to be assigned to new value

edited Sep 10, 2021 at 20:07

answered Sep 10, 2021 at 19:57

cuZzior

866 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

jwvh · Accepted Answer · 2021-09-10 21:13:28Z

1

It sounds like a ListMap is what you want.

From the ScalaDocs page: "Entries are stored internally in reversed insertion order, which means the newest key is at the head of the list."

So to transit from the current Map to a ListMap:

import scala.collection.immutable.ListMap

val newMap: ListMap[String,Time] = 
  oldMap.toList.sortBy{
    case (_, Time(d,h,m,s)) => (d,h,m,s)
  }.foldLeft(ListMap[String,Time]())(_+_)

testing:

newMap.head //res0: (NX-66-PP,Time(18492,3,6,30.0))
newMap.last //res1: (LA-53-NY,Time(18492,9,0,56.0))
newMap("MM-11-OW")    //res2: Time(18492,3,7,16.0)

edited Sep 10, 2021 at 21:13

answered Sep 10, 2021 at 20:14

jwvh

51.3k7 gold badges42 silver badges70 bronze badges

Collectives™ on Stack Overflow

How to sort 'Map' values in Scala against multiple factors?

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related