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  1. # Trying to figure out the behavior of numpy.interp.
  2.  
  3. import math
  4. import bisect
  5.  
  6. def to_float(iterable):
  7.     return list(map(float, iterable))
  8.  
  9. def lerp(a, b, t):
  10.     return (1 - t) * a + b * t
  11.  
  12. def invlerp(x, a, b):
  13.     if math.isclose(a, b):
  14.         return 0.5
  15.     return (x - a) / (b - a)
  16.  
  17. def interp(x, xp, fp, left=None, right=None):
  18.     """
  19.     Linear interpolation for monotonically increasing sample points.
  20.     """
  21.     n = len(xp)
  22.  
  23.     if n != len(fp):
  24.         raise ValueError('fp and xp are not of the same length.')
  25.     if n == 0:
  26.         return
  27.  
  28.     xp = to_float(xp)
  29.     fp = to_float(fp)
  30.  
  31.     if left is None:
  32.         left = fp[0]
  33.     else:
  34.         left = float(left)
  35.     if right is None:
  36.         right = fp[-1]
  37.     else:
  38.         right = float(right)
  39.  
  40.     last = xp[-1]
  41.  
  42.     for y in x:
  43.         if y > last:
  44.             yield right; continue
  45.         i = bisect.bisect(xp, y)
  46.         if i == 0:
  47.             yield left; continue
  48.         j = i-1
  49.         k = min(i, n-1)
  50.         yield lerp(fp[j], fp[k], invlerp(y, xp[j], xp[k]))
  51.  
  52. # Main.
  53.  
  54. xp = [1, 2, 3]
  55. fp = [3, 2, 0]
  56. x  = [0, 0.99, 1, 1.5, 2.73, 3, 3.01, 3.14]
  57.  
  58. print(list(interp([2.5], xp, fp)))
  59. print(list(interp(x, xp, fp)))
  60. print(list(interp(x, xp, fp, left=-99, right=99)))
  61.  
  62. import numpy as np
  63. print(list(np.interp([2.5], xp, fp)))
  64. print(list(np.interp(x, xp, fp)))
  65. print(list(np.interp(x, xp, fp, left=-99, right=99)))
Success #stdin #stdout 0.79s 41600KB
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stdin
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Standard input is empty
stdout
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[1.0]
[3.0, 3.0, 3.0, 2.5, 0.54, 0.0, 0.0, 0.0]
[-99.0, -99.0, 3.0, 2.5, 0.54, 0.0, 99.0, 99.0]
[1.0]
[3.0, 3.0, 3.0, 2.5, 0.54, 0.0, 0.0, 0.0]
[-99.0, -99.0, 3.0, 2.5, 0.54, 0.0, 99.0, 99.0]
https://ideone.com/7lMANz
language:
Python 3 (python  3.12)
created:
1 day ago
visibility:
public

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