1+ import random
2+ import math
3+
4+
5+ """
6+ 1: Logarithmic Weighted Random Selector
7+ """
8+ def lwrs (elements : list ):
9+ """
10+ Logarithmic Weighted Random Selector:
11+
12+ Gets a list of elements, and using a logarithmic scale,
13+ selects randomly one member of the list giving a higher
14+ probability weight to the initial elements of the list.
15+
16+ This algorithm has to select with more frecuency
17+ the initial members of the list, based on the
18+ logarithmic/exponential curve form.
19+
20+ Parameters:
21+ - elements [list or iter]: List of elements in order of importance.
22+ Returns:
23+ - Random element selected from the input list.
24+ """
25+
26+ #* Amount of elements: "n":
27+ n = len (elements )
28+
29+ #* Validation cases:
30+ if not hasattr (elements , "__iter__" ):
31+ raise TypeError (f"\" elements\" has to be a list or iterable, but given { type (elements )} )
32+ if n == 0 :
33+ raise ValueError ("\" elements\" is empty list. List" )
34+ if n == 1 :
35+ return elements [0 ]
36+
37+ #* Throws a random float number based on the n elements:
38+ #? To operate the numbers, it will consider 1 as the
39+ #? first element; then when it selects an index of the
40+ #? list, it will take at 0-starting notation:
41+ #/ Random float between 1 and n with 4 decimals.
42+ #* This random represent a random point of selection
43+ #* in a linear axis in which all elements has the same
44+ #* space to be selected:
45+ random_point = round (random .uniform (0 , n ), 4 )
46+ # print(f"\nLineal: {random_point}; ", end="")
47+
48+ """
49+ This is the propuse:
50+
51+ * Having a linear scale between 1 - n, all the spaces
52+ between elements has the same size.
53+
54+ * Having a logarithmic scale between 1 - n, the spaces
55+ between elements are different; the first element has
56+ the biggest space, the second is smaller, etc. The
57+ differences between the spaces is based on logarithms.
58+
59+ * When the random is selected, you get the linear scale
60+ element; then it has to ponderate the space with the
61+ logarithmic scale, to select the equivalent.
62+
63+ Example:
64+ NOTE: E1, E2, ..., E6 are the 6 elements of the list.
65+
66+ LINEAR SCALE:
67+ E1 E2 E3 E4 E5 E6
68+ 0 1 2 3 4 5 6
69+ |-------|-------|-------|-------|-------|-------|
70+
71+ RANDOM POINT:
72+ *
73+
74+ LOGARITHMIC SCALE:
75+ E1 E2 E3 E4 E5 E6
76+ 0 1 2 3 4 5 6
77+ |----------------|-----------|-------|----|---|-|
78+
79+ SELECTION:
80+
81+ * Linear: 3.24: [E4];
82+ * Logarithmic: 3: [E2];
83+
84+ """
85+
86+ #?// If the random is 1; it takes at defect the first element:
87+ # if random_point == 1:
88+ # return 0
89+
90+ #? The formula to calculate the distance between the start of
91+ #? the scale, and a randomLinear point, is:
92+ #/ logPoint = n*log_n+1(linearPoint);
93+ #/ The linearPoint has to be >= 2; and <= n+1:
94+ #* So, it starts a loop to check if the random linear point is
95+ #* between the space of the first log point, or the second, or
96+ #* the third, etc.
97+ for i in range (1 , n + 1 ):
98+ if random_point <= n * math .log (i + 1 , n + 1 ):
99+ return elements [i - 1 ]
100+
101+
102+ """
103+ 2: Exponential Weighted Random Selection
104+ """
105+ def ewrs (lista , base = 2 ):
106+
107+ #? Weights calcultation:
108+ wieghts = [base ** i for i in range (len (lista ))]
109+
110+ #? Order inversion of the weights:
111+ wieghts = wieghts [::- 1 ]
112+ total_weights = sum (wieghts )
113+
114+ #? Normalization to 1:
115+ probabilities = [weight / total_weights for weight in wieghts ]
116+
117+ #? Selection loop:
118+ random_point = random .uniform (0 , 1 )
119+ cumulative = 0
120+ for i , probability in enumerate (probabilities ):
121+ cumulative += probability
122+ if cumulative >= random_point :
123+ return lista [i ]
124+
125+
126+ """
127+ 3: Complexity Weighted Random Selector
128+ """
129+ def cwrs (elements : list , complexity : float ):
130+ """
131+ Select one element from the list "elements" based on a bias determined by the complexity value
132+ The weight is given by a power law decay:
133+ - w(i) = 1 / (i+1)^s
134+ where:
135+ - s = s_max * (1 - complexity/100)
136+ - s_max = (n / (n*(complexity/100))) * ((complexity/100)+1)
137+ - complexity is between 0 and 100
138+
139+ For complexity=0, s = n (maximum steepness) and the first element is nearly always selected
140+ For complexity=1, s = 0 and all elements have weight 1 (uniform selection)
141+ """
142+ n = len (elements )
143+ if complexity < 0 and complexity > 1 :
144+ raise ValueError ("\" complexity\" must be between 0 and 100" )
145+
146+ if complexity == 0 :
147+ s_max = n
148+ else :
149+ s_max = (n / (n * (complexity / 100 ))) * ((complexity / 100 )+ 1 )
150+
151+ s = s_max * (1 - complexity / 100.0 )
152+
153+ # Compute weights for each element using the power law:
154+ weights = [1 / ((i + 1 ) ** s ) for i in range (n )]
155+
156+ # Normalize the weights to get a probability distribution:
157+ total = sum (weights )
158+ probabilities = [w / total for w in weights ]
159+
160+ return random .choices (elements , weights = probabilities , k = 1 )[0 ]
0 commit comments