Sorrting Elements In Map Collection Based On Value

[KWSW]

I need to sort out based on frequency certain events that happen.

I use a map with the event name as the key(String) and the frequency(Integer) as the value and every time an event happens.

I have no problems with the part of adding and updating but am abit stuck at the sorting part as I need to display the events sorted from higest frequency to lowest.

At first I was thinking of putting them into another hashmap with the frequency as the key as it auto sorts based on key but if I have 2 or more events with the same frequency, I might overwrite them.

TIA :)

[JosAH]

I need to sort out based on frequency certain events that happen.

I use a map with the event name as the key(String) and the frequency(Integer) as the value and every time an event happens.

I have no problems with the part of adding and updating but am abit stuck at the sorting part as I need to display the events sorted from higest frequency to lowest.

At first I was thinking of putting them into another hashmap with the frequency as the key as it auto sorts based on key but if I have 2 or more events with the same frequency, I might overwrite them.

TIA :)

So now you have a Map<String, Integer> where the keys are Strings and the
frequencies are Integers.

Build another map like this: Map<Integer, List<String>> and add your value, key
pairs (frequencies, keys) like this:

 
// the 'inverted' map
private Map<Integer>, List<String>>= new TreeMap<Integer, List<String>>();
...
public void add(Integer freq, String key) {
   List<String> list= map.get(freq);
   if (list == null) map.put(freq, list= new ArrayList<String>());
   list.add(key);
}
 

That's all there is to it ;-)

kind regards,

Jos

[KWSW]

So now you have a Map<String, Integer> where the keys are Strings and the
frequencies are Integers.

Build another map like this: Map<Integer, List<String>> and add your value, key
pairs (frequencies, keys) like this:

 
// the 'inverted' map
private Map<Integer>, List<String>>= new TreeMap<Integer, List<String>>();
...
public void add(Integer freq, String key) {
   List<String> list= map.get(freq);
   if (list == null) map.put(freq, list= new ArrayList<String>());
   list.add(key);
}
 

That's all there is to it ;-)

kind regards,

Jos

ok will try it out...

btw it will be from the lowest to highest right? Is there anyway to get from the back or sort it the other way around since I need the highest frequency?

[JosAH]

ok will try it out...

btw it will be from the lowest to highest right? Is there anyway to get from the back or sort it the other way around since I need the highest frequency?

Use -frequency for the key values? This is just a quick hack.

kind regards,

Jos

[KWSW]

Use -frequency for the key values? This is just a quick hack.

kind regards,

Jos

thanks again... it works... one last qn(hopefully)...

I know i can use

for(Int i : map.keyset())

to go through the whole map, but if I want to just take out the first ten, is there another type of for loop to do it?

[JosAH]

thanks again... it works... one last qn(hopefully)...

I know i can use

for(Int i : map.keyset())

to go through the whole map, but if I want to just take out the first ten, is there another type of for loop to do it?

Sure, use a counter and when it reaches the value 10 break out of the loop
(there are more ways to skin this cat though).

kind regards,

Jos