Interpolation

numbergrid.py

#!/usr/bin/env python3
'''Interpolates numeric datasets'''

import sortedcontainers

def mix(a, b, ratio):
  '''Return a if raio is 0, b if ratio is 1, and between a and b for a ratio inbetween.'''
  return a + (b - a) * ratio

def interpolate(sorted_container, interval):
  '''Interpolate a sorted container with linear blending'''
  start_key = sorted_container.iloc[0]
  end_key = sorted_container.iloc[-1]
  this_key = start_key
  output = sortedcontainers.SortedDict()

  while this_key <= end_key:

    # Copy over an item if it already exists, and the two end points
    if this_key in sorted_container \
        or this_key == start_key \
        or this_key == end_key:
      output[this_key] = sorted_container[this_key]

    # Locate the nearest two data points and interpolate
    else:

      # Find the two items between this data point, and get their distances
      left_index = sorted_container.bisect(this_key) - 1
      right_index = sorted_container.bisect(this_key)

      left_key = sorted_container.peekitem(left_index)[0]
      right_key = sorted_container.peekitem(right_index)[0]

      # Blend the left and right using the ratio of two distances
      ratio = (right_key - this_key) / (right_key - left_key)
      left = sorted_container.peekitem(left_index)[1]
      right = sorted_container.peekitem(right_index)[1]
      inbetween = mix(left, right, ratio)

      output[this_key] = inbetween

    this_key += interval

  return output