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By: a guest on Apr 29th, 2012  |  syntax: None  |  size: 0.98 KB  |  hits: 10  |  expires: Never
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  1. Elegant pythonic cumsum
  2. >>> import numpy as np
  3. >>> np.cumsum([1,2,3,4,5])
  4. array([ 1,  3,  6, 10, 15])
  5.        
  6. def cumsum(it):
  7.     total = 0
  8.     for x in it:
  9.         total += x
  10.         yield total
  11.        
  12. >>> list(cumsum([1,2,3,4,5]))
  13. >>> [1, 3, 6, 10, 15]
  14.        
  15. a=[1,2,3,4,5]
  16.  
  17. def cumsum(a):
  18.     a=iter(a)
  19.     cc=[next(a)]
  20.     for i in a:
  21.         cc.append(cc[-1]+i)
  22.     return cc
  23.  
  24. print cumsum(a)
  25. "[1, 3, 6, 10, 15]"
  26.        
  27. a=[1,2,3,4,5]
  28. def cumsum(a):
  29.     for i in range(1,len(a)):
  30.         a[i]+=a[i-1]
  31.  
  32. cumsum(a)
  33. print a
  34. "[1, 3, 6, 10, 15]"
  35.        
  36. a = [1, 2, 3 ,4, 5]
  37.  
  38. # Using list comprehention
  39. cumsum = [sum(a[:i+1]) for i in range(len(a))]           # [1, 3, 6, 10, 15]
  40.  
  41. # Using map()
  42. cumsum = map(lambda i:  sum(a[:i+1]), range(len(a)))     # [1, 3, 6, 10, 15]
  43.        
  44. def cumsum(vec):
  45.     r = [vec[0]]
  46.     for val in vec[1:]:
  47.         r.append(r[-1] + val)
  48.     return r
  49.        
  50. a=[1,2,3,4,5]
  51. def cumsum(a):
  52.     b=a[:]
  53.     for i in range(1,len(a)):
  54.         b[i]+=b[i-1]
  55.     return b
  56.  
  57. print cumsum(a)
  58. "[1, 3, 6, 10, 15]"
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