Examples of QuantileBin1D

• hep.aida.bin.QuantileBin1D
  ad.eecs.berkeley.edu/~manku/papers/unknown.ps.gz"> here.

  and

  Gurmeet Singh Manku, Sridhar Rajagopalan and Bruce G. Lindsay, Approximate Medians and other Quantiles in One Pass and with Limited Memory, Proc. of the 1998 ACM SIGMOD Int. Conf. on Management of Data, Paper available here.

  The broad picture is as follows. Two concepts are used: Shrinking and Sampling. Shrinking takes a data sequence, sorts it and produces a shrinked data sequence by picking every k-th element and throwing away all the rest. The shrinked data sequence is an approximation to the original data sequence.

  Imagine a large data sequence (residing on disk or being generated in memory on the fly) and a main memory block of n=b*k elements (b is the number of buffers, k is the number of elements per buffer). Fill elements from the data sequence into the block until it is full or the data sequence is exhausted. When the block (or a subset of buffers) is full and the data sequence is not exhausted, apply shrinking to lossily compress a number of buffers into one single buffer. Repeat these steps until all elements of the data sequence have been consumed. Now the block is a shrinked approximation of the original data sequence. Treating it as if it would be the original data sequence, we can determine quantiles in main memory.

  Now, the whole thing boils down to the question of: Can we choose b and k (the number of buffers and the buffer size) such that b*k is minimized, yet quantiles determined upon the block are guaranteed to be away from the true quantiles no more than some epsilon? It turns out, we can. It also turns out that the required main memory block size n=b*k is usually moderate (see the table above).

  The theme can be combined with random sampling to further reduce main memory requirements, at the expense of probabilistic guarantees. Sampling filters the data sequence and feeds only selected elements to the algorithm outlined above. Sampling is turned on or off, depending on the parametrization.

  This quick overview does not go into important details, such as assigning proper weights to buffers, how to choose subsets of buffers to shrink, etc. For more information consult the papers cited above.

  Time Performance:

  Pentium Pro 200 Mhz, SunJDK 1.2.2, NT, java -classic,
  filling 10 ⁴ elements at a time, reading 100 percentiles at a time,
  hasSumOfLogarithms()=false, hasSumOfInversions()=false, getMaxOrderForSumOfPowers()=2
  

  Performance
  Quantiles	Epsilon	Delta		Filling [#elements/sec]			Quantile computation [#quantiles/sec]
  				N unknown, Nmax=inf	N known, Nmax=107		N unknown, Nmax=inf	N known, Nmax=107
  104	10 -1	10 -1		1600000	1300000		250000	130000
  	10 -2			360000	1200000		50000	20000
  	10 -3			150000	200000		3600	3000
  	10 -4			120000	170000		80	1000

  @see cern.jet.stat.quantile @author wolfgang.hoschek@cern.ch @version 0.9, 03-Jul-99

Examples of hep.aida.bin.QuantileBin1D

Examples of hep.aida.bin.QuantileBin1D