Velocity Reviews > Java > SortedMap: getting value for largest key less or equal a given

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

Andreas Leitgeb
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Posts: n/a

 08-02-2012
From: Andreas Leitgeb <(E-Mail Removed)>

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.

// 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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Andreas Leitgeb
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Posts: n/a

 08-02-2012
To: Andreas Leitgeb
From: Andreas Leitgeb <(E-Mail Removed)>

Andreas Leitgeb <(E-Mail Removed)> 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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markspace
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Posts: n/a

 08-02-2012
To: Andreas Leitgeb
From: markspace <-@.>

On 8/1/2012 1:19 PM, Andreas Leitgeb wrote:
> Andreas Leitgeb <(E-Mail Removed)> 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.

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Roedy Green
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Posts: n/a

 08-02-2012
To: markspace
From: Roedy Green <(E-Mail Removed)>

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.

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.
--
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)

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Daniel Pitts
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Posts: n/a

 08-02-2012
To: Roedy Green
From: Daniel Pitts <(E-Mail Removed)>

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.

>
> 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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Andreas Leitgeb
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Posts: n/a

 08-03-2012
To: Daniel Pitts
From: Andreas Leitgeb <(E-Mail Removed)>

Daniel Pitts <(E-Mail Removed)> 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...

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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