diff --git a/code/lib/lmdk_bgt.py b/code/lib/lmdk_bgt.py index ce72de4..a12bb37 100644 --- a/code/lib/lmdk_bgt.py +++ b/code/lib/lmdk_bgt.py @@ -1,5 +1,6 @@ #!/usr/bin/env python3 +from datetime import datetime from geopy.distance import distance import math import numpy as np @@ -420,6 +421,52 @@ def sample(seq, lmdks, epsilon): return rls_data, bgts, skipped +def discount(seq, lmdks, epsilon): + ''' + Temporally discounted sampling. + + Parameters: + seq - The point sequence. + lmdks - The landmarks. + epsilon - The available privacy budget. + Returns: + rls_data - The perturbed data. + bgts - The privacy budget allocation. + skipped - The number of skipped releases. + ''' + # Uniform budget allocation + bgts = uniform(seq, lmdks, epsilon) + # Released + rls_data = [None]*len(seq) + # Track landmarks + lmdk_cur = 0 + # Track skipped releases + skipped = 0 + for i, p in enumerate(seq): + # The sampling rate + samp_rt = datetime.fromtimestamp(int(lmdks[lmdk_cur][3]))/datetime.fromtimestamp(int(lmdks[len(lmdks) - 1][3])) + # Check if current point is a landmark + if lmdk_lib.is_landmark(p, lmdks): + lmdk_cur += 1 + # Get coordinates + loc = (p[1], p[2]) + if i == 0 or lmdk_lib.should_sample(samp_rt): + # Add noise to original data + new_loc = lmdk_lib.add_polar_noise(loc, bgts[i]) + rls_data[i] = [p[0], new_loc[0], new_loc[1], p[3]] + else: + skipped += 1 + # Skip current release and approximate with previous + rls_data[i] = rls_data[i - 1] + if lmdk_lib.is_landmark(p, lmdks): + # Allocate the current budget to the following releases uniformly + for j in range(i + 1, len(seq)): + bgts[j] += bgts[i]/(len(lmdks) - lmdk_cur + 1) + # No budget was spent + bgts[i] = 0 + return rls_data, bgts, skipped + + def uniform_r(seq, lmdks, epsilon): # Released rls_data = [None]*len(seq)