ML.InfoTheory.BitRank

Package ML :: Package InfoTheory :: Module BitRank |
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# Source Code for Module ML.InfoTheory.BitRank

      1  #
      2  #  Copyright (C) 2001,2002,2003  greg Landrum and Rational Discovery LLC
      3  #
      4  """ Functionality for ranking bits using info gains
      5
      6   **Definitions used in this module**
      7
      8      - *sequence*: an object capable of containing other objects which supports
      9        __getitem__() and __len__().  Examples of these include lists, tuples, and
     10        Numeric arrays.
     11
     12      - *IntVector*: an object containing integers which supports __getitem__() and
     13         __len__(). Examples include lists, tuples, Numeric Arrays, and BitVects.
     14
     15
     16   **NOTE**: Neither *sequences* nor *IntVectors* need to support item assignment.
     17     It is perfectly acceptable for them to be read-only, so long as they are
     18     random-access.
     19
     20  """
     21  import numpy
     22  from ML.InfoTheory import entropy
     23
     24 -def FormCounts(bitVects,actVals,whichBit,nPossibleActs,nPossibleBitVals=2):
     25    """ generates the counts matrix for a particular bit
     26
     27    **Arguments**
     28
     29      - bitVects: a *sequence* containing *IntVectors*
     30
     31      - actVals: a *sequence*
     32
     33      - whichBit: an integer, the bit number to use.
     34
     35      - nPossibleActs: the (integer) number of possible activity values.
     36
     37      - nPossibleBitVals: (optional) if specified, this integer provides the maximum
     38        value attainable by the (increasingly inaccurately named) bits in _bitVects_.
     39
     40    **Returns**
     41
     42      a Numeric array with the counts
     43
     44    **Notes**
     45
     46      This is really intended for internal use.
     47
     48    """
     49    if len(bitVects) != len(actVals): raise ValueError,'var and activity lists should be the same length'
     50    res = numpy.zeros((nPossibleBitVals,nPossibleActs),numpy.integer)
     51    for i in xrange(len(bitVects)):
     52      res[bitVects[i][whichBit],actVals[i]] += 1
     53    return res
     54
     55 -def CalcInfoGains(bitVects,actVals,nPossibleActs,nPossibleBitVals=2):
     56    """  Calculates the information gain for a set of points and activity values
     57
     58    **Arguments**
     59
     60      - bitVects: a *sequence* containing *IntVectors*
     61
     62      - actVals: a *sequence*
     63
     64      - nPossibleActs: the (integer) number of possible activity values.
     65
     66      - nPossibleBitVals: (optional) if specified, this integer provides the maximum
     67        value attainable by the (increasingly inaccurately named) bits in _bitVects_.
     68
     69     **Returns**
     70
     71       a list of floats
     72
     73    """
     74    if len(bitVects) != len(actVals): raise ValueError,'var and activity lists should be the same length'
     75    nBits = len(bitVects[0])
     76    res = numpy.zeros(nBits,Float)
     77
     78    for bit in xrange(nBits):
     79      counts = FormCounts(bitVects,actVals,bit,nPossibleActs,
     80                          nPossibleBitVals=nPossibleBitVals)
     81      res[bit] = entropy.InfoGain(counts)
     82    return res
     83
     84 -def RankBits(bitVects,actVals,nPossibleBitVals=2,
     85               metricFunc=CalcInfoGains):
     86    """ Rank a set of bits according to a metric function
     87
     88    **Arguments**
     89
     90      - bitVects: a *sequence* containing *IntVectors*
     91
     92      - actVals: a *sequence*
     93
     94      - nPossibleBitVals: (optional) if specified, this integer provides the maximum
     95        value attainable by the (increasingly inaccurately named) bits in _bitVects_.
     96
     97      - metricFunc: (optional) the metric function to be used.  See _CalcInfoGains()_
     98        for a description of the signature of this function.
     99
    100     **Returns**
    101
    102       A 2-tuple containing:
    103
    104         - the relative order of the bits (a list of ints)
    105
    106         - the metric calculated for each bit (a list of floats)
    107
    108    """
    109    nPossibleActs = max(actVals)+1
    110    metrics = metricFunc(bitVects,actVals,nPossibleActs,
    111                         nPossibleBitVals=nPossibleBitVals)
    112    bitOrder = list(numpy.argsort(metrics))
    113    bitOrder.reverse()
    114    return bitOrder,metrics
    115
    116
    117 -def AnalyzeSparseVects(bitVects,actVals):
    118    """ #DOC
    119
    120    **Arguments**
    121
    122      - bitVects: a *sequence* containing SBVs
    123
    124      - actVals: a *sequence*
    125
    126     **Returns**
    127
    128       a list of floats
    129
    130     **Notes**
    131
    132        - these need to be bit vects and binary activities
    133
    134    """
    135    nPts = len(bitVects)
    136    if nPts != len(actVals): raise ValueError,'var and activity lists should be the same length'
    137    nBits = bitVects[0].GetSize()
    138
    139    actives = numpy.zeros(nBits,numpy.integer)
    140    inactives = numpy.zeros(nBits,numpy.integer)
    141    nActives,nInactives = 0,0
    142    for i in range(nPts):
    143      sig,act = bitVects[i],actVals[i]
    144      onBitList = sig.GetOnBits()
    145      if act:
    146        for bit in onBitList:
    147          actives[bit] += 1
    148        nActives += 1
    149      else:
    150        for bit in onBitList:
    151          inactives[bit] += 1
    152        nInactives += 1
    153    resTbl = numpy.zeros((2,2),numpy.integer)
    154    res = []
    155    gains = []
    156    counts = []
    157    for bit in xrange(nBits):
    158      nAct,nInact = actives[bit],inactives[bit]
    159      if nAct or nInact:
    160        resTbl[0,0] = nAct
    161        resTbl[1,0] = nPts - nAct
    162        resTbl[0,1] = nInact
    163        resTbl[1,1] = nPts - nInact
    164        gain = entropy.InfoGain(resTbl)
    165        gains.append(gain)
    166        res.append((bit,gain,nAct,nInact))
    167    return res,gains
    168
    169 -def SparseRankBits(bitVects,actVals,metricFunc=AnalyzeSparseVects):
    170    """ Rank a set of bits according to a metric function
    171
    172    **Arguments**
    173
    174      - bitVects: a *sequence* containing SBVs
    175
    176      - actVals: a *sequence*
    177
    178      - metricFunc: (optional) the metric function to be used.  See _SparseCalcInfoGains()_
    179        for a description of the signature of this function.
    180
    181     **Returns**
    182
    183       A 2-tuple containing:
    184
    185         - the relative order of the bits (a list of ints)
    186
    187         - the metric calculated for each bit (a list of floats)
    188
    189      **Notes**
    190
    191        - these need to be bit vects and binary activities
    192
    193    """
    194    info,metrics = metricFunc(bitVects,actVals)
    195    bitOrder = list(numpy.argsort(metrics))
    196    bitOrder.reverse()
    197    return bitOrder,info
    198