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SortedMap: getting value for largest key less or equal a given value...

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  SortedMap: getting value for largest key less or equal a given value... Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-08-01 19:45 +0000
    Re: SortedMap: getting value for largest key less or equal a given value... Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-08-01 20:19 +0000
      Re: SortedMap: getting value for largest key less or equal a given value... markspace <-@.> - 2012-08-01 14:48 -0700
        Re: SortedMap: getting value for largest key less or equal a given value... Roedy Green <see_website@mindprod.com.invalid> - 2012-08-02 01:20 -0700
          Re: SortedMap: getting value for largest key less or equal a given value... Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-08-02 09:53 -0700
            Re: SortedMap: getting value for largest key less or equal a given value... Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2012-08-03 00:55 +0000

#16941 — SortedMap: getting value for largest key less or equal a given value...

I've got an approach like the following, but I'm not entirely
happy with it. (see embedded comments)
Error checking left out only for brevity-of-post's sake.

<sscce>
class StepFunction<K,V> {
   SortedMap<K,V> m_map = new TreeMap<K,V>();
   public void put(K k,V v) { m_map.put(k,v); } // for demo-fill
   
   /** @return the value for the largest key in the map
          that is less OR equal to the given parameter.  */

   public V value(K k) {
      // not really correct for generic use. In my usecase, K is
      //  actually Long, so I just add one to k to make it work.
      return m_map.get(m_map.headMap(k).lastKey());

      // I'm a bit unhappy about headMap's "open end",
      // and also about the lack of some method like
      //   lastEntry() or lastKeysValue() in SortedMap,
      // requiring one to look up the lastKey in the map,
      // although the map had "its finger on it" just before.
      //   Did I miss something simple and obvious?
   }
   // demo-helper
   void checkVal(K k, V v) {
      System.out.println( map.value(k) + " should be " + v);
   }
   public static void main(String[] args) {
      StepFunction<Integer,Double> sf = new StepFunction<>()
      sf.put(Integer.MIN_VALUE, -1.0);
      sf.put(0, 0.0); sf.put(2, 1.0);

      sf.checkVal(-1 , -1.0);
      sf.checkVal( 0 ,  0.0);
      sf.checkVal( 1 ,  0.0);
      sf.checkVal( 2 ,  1.0);
      sf.checkVal(Integer.MAX_VALUE , 1.0);
   }
}
</sscce>

PS: No need to offer "solutions" involving linear search.
  I could have come up with one, myself, if I wanted one.  

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#16942

Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> wrote:
> I've got an approach like the following, but I'm not entirely
> happy with it...

It took me about an hour to compose that previous post, and not
only did a bug still hide in it ("map" instead of "m_map"), but
also: only five minutes after posting, it occurred to me that I
could also look at TreeMap's methods, rather than only at
SortedMap's, and thereby stumbled over the (new in 1.6) interface
NavigableMap.

PS: return m_map.floorEntry(k).getValue(); // :-)
Case closed.

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#16943

On 8/1/2012 1:19 PM, Andreas Leitgeb wrote:
> Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> wrote:
>> I've got an approach like the following, but I'm not entirely
>> happy with it...
>
> It took me about an hour to compose that previous post, and not
> only did a bug still hide in it ("map" instead of "m_map"), but
> also: only five minutes after posting, it occurred to me that I
> could also look at TreeMap's methods, rather than only at
> SortedMap's, and thereby stumbled over the (new in 1.6) interface
> NavigableMap.
>
> PS: return m_map.floorEntry(k).getValue(); // :-)
> Case closed.


It is my contention that any requests for help should contain a careful 
explanation of the problem and attempted solutions, plus an SSCCE.  Then 
the author should save the request on disc and go to lunch.  If no 
solution was discovered during lunch, then the request should be sent.

I think there's a Dilbert cartoon about this.

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#16955

On Wed, 01 Aug 2012 14:48:20 -0700, markspace <-@.> wrote, quoted or
indirectly quoted someone who said :

>save the request on disc and go to lunch.

Bertrand Russell "told" me about this years ago.  You have to get away
from your computer. He suggested even a week of "not" thinking about
it for a toughie. Then when you revisit the problem, the answer will
be right under your nose.

I just think about the problem while walking.  The details are cleared
away so I have to think more abstractly. I ask myself , what could be
failing that created those symptoms.  I am not looking for particular
code, just thinking about code that does some function.  It is a
different sort of thinking than trying to decide if a line of code is
faulty.

Of course Murphy's law says the most likely time for the answer to
come to you is one second after hitting submit.
-- 
Roedy Green Canadian Mind Products
http://mindprod.com
The greatest shortcoming of the human race is our inability to understand the exponential function. 
 ~ Dr. Albert A. Bartlett (born: 1923-03-21 age: 89)
http://www.youtube.com/watch?v=F-QA2rkpBSY

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#16964

On 8/2/12 1:20 AM, Roedy Green wrote:
> On Wed, 01 Aug 2012 14:48:20 -0700, markspace <-@.> wrote, quoted or
> indirectly quoted someone who said :
>
>> save the request on disc and go to lunch.
>
> Bertrand Russell "told" me about this years ago.  You have to get away
> from your computer. He suggested even a week of "not" thinking about
> it for a toughie. Then when you revisit the problem, the answer will
> be right under your nose.
>
> I just think about the problem while walking.  The details are cleared
> away so I have to think more abstractly. I ask myself , what could be
> failing that created those symptoms.  I am not looking for particular
> code, just thinking about code that does some function.  It is a
> different sort of thinking than trying to decide if a line of code is
> faulty.
>
> Of course Murphy's law says the most likely time for the answer to
> come to you is one second after hitting submit.
If we're talking about Murphy, then by submit you mean "deploy the hack 
workaround fix to production after a month of QA".

;-)

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#17018

Daniel Pitts <newsgroup.nospam@virtualinfinity.net> wrote:
> On 8/2/12 1:20 AM, Roedy Green wrote:
>> On Wed, 01 Aug 2012 14:48:20 -0700, markspace <-@.> wrote, quoted or
>> indirectly quoted someone who said :
>>> save the request on disc and go to lunch.

I hardly ever go to lunch at all. Typically have a bite at the workplace...

>> Bertrand Russell "told" me about this years ago.  You have to get away
>> from your computer.

Away from the computer I couldn't have had a look at TreeMap's methods...

>> He suggested even a week of "not" thinking about it for a toughie.

Within a week of this strategy, surely one of the coworkers would have noticed
my inactivity on the task and taken it over... maybe eventually asking me what
I think I'm being paid for...   Nope, rather not let that happen ;-)

>> Of course Murphy's law says the most likely time for the answer to
>> come to you is one second after hitting submit.
Good description of what kind of happened, btw.

> If we're talking about Murphy, then by submit you mean "deploy the hack 
> workaround fix to production after a month of QA".
> ;-)
;-)

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