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A collection of some useful list-related functions.

Python, 162 lines
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#========================================================================
def sumList(L):
    return reduce(lambda x,y:x+y, L)

#========================================================================
def avgList(L):
    return reduce(lambda x,y:x+y, L) /(len(L)*1.0)

#========================================================================
def normList(L, normalizeTo=1):
    '''normalize values of a list to make its max = normalizeTo'''

    vMax = max(L)
    return [ x/(vMax*1.0)*normalizeTo for x in L]

#========================================================================
def normListSumTo(L, sumTo=1):
    '''normalize values of a list to make it sum = sumTo'''

    sum = reduce(lambda x,y:x+y, L)
    return [ x/(sum*1.0)*sumTo for x in L]

#========================================================================
def accumList(L, normalizeTo=None):
    ''' L= [1, 2, 3,  4,  5]:        accumList(L)=> [1, 3, 6, 10, 15] 
        L= [0.25, 0.25, 0.25, 0.25]: accumList(L)=> [0.25, 0.50, 0.75, 1.00]
        normalizeTo: set the last number of the returned list to this value
    '''
    
    if normalizeTo: LL = normListSumTo(L, sumTo=normalizeTo)
    else: LL = L[:]

    r = range(1, len(LL))
    newList=[LL[0]]
    for i in r:
        newList.append( newList[-1]+ LL[i] )
    return newList

#========================================================================
def findIndex(sortedList, x, indexBuffer=0):
  ''' Given a sortedList and value x, return the index i where
      sortedList[i-1] <= x < sortedList[i]

      Which means,
        sortedList.insert( findIndex(sortedList, x), x )
      will give a sorted list  
  '''

  if len(sortedList)==2:
    
    if x==sortedList[-1]:   return indexBuffer+2
    elif x>=sortedList[0]:  return indexBuffer+1

  else:
    L = len(sortedList)  
    firstHalf  = sortedList[:L/2+1]
    secondHalf = sortedList[(L/2):]

    if secondHalf[-1]<=x:
      return indexBuffer + len(sortedList)
    elif x< firstHalf[0]:
      return indexBuffer
    else:
      if firstHalf[-1] < x:
        return findIndex(secondHalf, x, indexBuffer=L/2+indexBuffer)
      else:
        return findIndex(firstHalf,x, indexBuffer=indexBuffer)

#========================================================================
def randomPickList(L):
    ''' given a list L, with all values are numbers,
        randomly pick an item and return it's index according
        to the percentage of all values'''

    return findIndex(accumList(L,1), random.random())

#========================================================================
def deepList(LString):
    '''
    Given string representation of a nested list tree,
    return a list containing all the deepest list contents.

    For example:

    '[[1,[2, 2a]],[[3,3b],4]]'
    ==> ['2, 2a', '3,3b']

    '[[[1,[2, 2a]],[[3,3b],4]],6]'
    ==> ['2, 2a', '3,3b']

    '[[[[a1,a2],out],o1],[o2,o3]]'
    ==> ['a1,a2', 'o2,o3']

    '[[[[[a1,a2], out], [o1,o2]],[o3,o4]],[o5,o6]]'
    ==> ['a1,a2', 'o1,o2', 'o3,o4', 'o5,o6']

    The code: [x.split(']') for x in code.split('[')]
    returns something like:
    [[''], [''], [''], [''], [''], ['a1,a2', ', out', ', '],
    ['o1,o2', '', ','], ['o3,o4', '', ','], ['o5,o6', '', '']]

    '''
    result= [x[0] for x in \
            [x.split(']') for x in LString.split('[')] \
            if len(x)>1]
    if result==['']: result =[]
    return result


#========================================================================
def getListStartsWith(aList, startsWith, isStrip=1):
    ''' for a list:   L= ['abcdef', 'kkddff', 'xyz', '0wer'...],

        getListStartWith(L, 'kk') will return:
           ['kkddff', 'xyz', '0wer'...],

        getListStartWith(L, 'xy') will return:
           ['xyz', '0wer'...],

        if isStrip: any item '  xyz' will be considered 'xyz'
        else:       the spaces in '  xyz' count.
           
    '''
    tmp = aList[:]
    if isStrip: tmp = [x.strip() for x in tmp]
    startLineIndex = 0
    for i in range(len(tmp)):
        if tmp[i].startswith(startsWith):
            startLineIndex = i
    return aList[startLineIndex:]

#========================================================================
def rezip(aList):
    ''' d = [[1, 5, 8, 3], [2, 2, 3, 9], [3, 2, 4, 6]]
        rezip(d):
        [(1, 2, 3), (5, 2, 2), (8, 3, 4), (3, 9, 6)]

    If a =[1, 5, 8], b=[2, 2, 3], c=[3, 2, 4]
    then it's eazy to: zip(a,b,c) = [(1, 2, 3), (5, 2, 2), (8, 3, 4)]

    But it's hard for d = [[1, 5, 8], [2, 2, 3], [3, 2, 4]]    
    '''

    tmp = [ [] for x in range(len(aList[0])) ]
    for i in range(len(aList[0])):
        for j in range(len(aList)):
            tmp[i].append(aList[j][i])
    return tmp

#========================================================================
def sumInList(complexList):
  ''' Given a complexList [ [a1,b1,c1], [a2,b2,c2], [a3,b3,c3] ],
      return a list [ a, b, c] where a = a1+a2+a3, etc.'''
  d = rezip(complexList)
  return [ reduce(lambda x,y:x+y, z) for z in d ]

#========================================================================
def avgInList(complexList):
  ''' Given a complexList [ [a1,b1,c1], [a2,b2,c2], [a3,b3,c3] ],
      return a list [ a, b, c] where a = avg of a1, a2, a3, etc.'''
  d = rezip(complexList)
  return [ reduce(lambda x,y:x+y, z)/(len(z)*1.0) for z in d ]

Among the above, randomPickList() is probably the most useful:


Testing randomPickList():

x= [1, 3, 6] Randomly pick an item from x for 1000 times to see the ratio in x is kept:

y = [0,0,0] for i in range(1000): y[randomPickList(x)]+=1

y=> [112, 300, 588]

2 comments

Simon Brunning 17 years, 7 months ago  # | flag

reZip. reZip can be simplified, I think:

def reZip(aList):
    return zip(*aList)

I usually call this function 'pivot'.

This returns a list of tupes, rather than a list of lists. If that matters, you could do:

def reZip(aList):
    return [list(tup) for tup in zip(*aList)]
Stefan Quandt 17 years, 7 months ago  # | flag

What about splitting a list? Is their an efficient way to split a list into two, equivalent to the code snippet below?

a = [ x for x in List if 'a' in x ]
b = [ x for x in List if not 'a' in x ]
Created by Runsun Pan on Wed, 14 Apr 2004 (PSF)
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