examples/ohritem.py

   1 """
   2 OHRRPGCE/FF6 style random item selection (percentage probability based)
   3 """
   4
   5 from ion.n.random import percent
   6 def got_item (info):
   7     """ Illustrates OHRRPGCE's behaviour giving items after battle.
   8     XXX make this into an example.
   9     Pass a tuple (item, item %, rareitem, rareitem %) as the info parameter.
  10
  11
  12     Returns
  13     -------
  14     item : object
  15            One of (item, rareitem, -1) (where -1 indicates nothing dropped)
  16
  17     Notes
  18     -----
  19     equivalent to::
  20
  21       tmp = chain (((item %, item), (rareitem %, rareitem)))
  22       if tmp:
  23         return tmp[-1]
  24       return -1
  25
  26     """
  27
  28     if percent (info[1]):
  29         # rareitem's chance to drop:
  30         # (100% - item%) * rareitem%
  31         #
  32         # eg. item% == 50, rareitem% == 50
  33         # drop item 25% of the time,
  34         # rareitem  25% of the time,
  35         # nothing   50% of the time.
  36         #
  37         # with rareitem% == 25:
  38         #  item     37.5%
  39         #  rareitem 12.5%
  40         #  nothing  50%
  41         #
  42         if percent ((info[3] * (100 - info[1])) / 100 ):
  43             return info[2] # rareitem
  44         else:
  45             return info[0] # item
  46     else:
  47         return -1 # nothing :(
  48
  49     # expressed in weighted sampling:
  50     #
  51     # remainder = float (100 - info[1])
  52     #
  53     # return weightedSample ((info[0],info[2], -1), (info[1],
  54     # (remainder / 2.0) * (info[3]/100.0), remainder / 2.0)
  55
  56     # In more general, weighting is like:
  57     #     item @ item%
  58     #     item2 @ remainder
  59     #     item3 @ i2remainder
  60     #     item4 @ i3remainder
  61     #     None  @ allremainder
  62     #
  63     # With remainders weighted into the previous remainder space.
  64     #
  65     #
  66     # say, 50% 40% 30% 20%
  67     #
  68     # then..
  69     # 50% chance of 1
  70     # 20% (40% * 50%) chance of 2
  71     # 8% (30% * (100% - (50% + 20%))) chance of 3
  72     # 4.2% chance (20% * (100% - (50% + 20% + 8%)) ) of 4
  73     # 16.8% chance (20% * (100% - (50% + 20% + 8% + 4.2%)) ) of None
  74     #
  75     # to be precise (percentages expressed like 1.00 == 100%)
  76     #
  77     # weights = []
  78     # weights.append (factorlist[0])
  79     # factorlist.pop(0)
  80     #
  81     # for fac in factorlist:
  82     #     weights.append ((fac / 100.0) * (100.0 - sum(weights)))
  83     #
  84     # weights.append (100.0 - sum(weights))
  85     #
  86     # examples:
  87     #
  88     #
  89
  90
  91
  92 # a dictionary mapping number -> name
  93 lut = {
  94     -1: "Nothing",
  95     1: "Item",
  96     2: "RareItem",
  97 }
  98
  99 print '100, 100:'
 100 #give item, never rareitem or nothing:
 101 for i in range (16):
 102     print lut[ got_item ((1, 100, 2, 100))]
 103
 104
 105 print '\n\n50, 50:'
 106 # give item 50% of the time, rareitem 25% of the time,
 107 # or nothing 25% of the time:
 108 for i in range (32):
 109     print lut[ got_item ((1, 50, 2, 50))]
 110
 111
 112 print '\n\n75, 33:'
 113 # give item 75% of the time, rareitem 8% of the time,
 114 # or nothing 17% of the time:
 115
 116 for i in range (32):
 117     print lut[ got_item ((1, 75, 2, 33))]
 118
 119