-
Notifications
You must be signed in to change notification settings - Fork 19
/
lttb.py
108 lines (88 loc) · 3.82 KB
/
lttb.py
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
"""
The MIT License (MIT)
Copyright (c) 2015 Olivier Devoisin
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
"""
import math
class LttbException(Exception):
pass
def largest_triangle_three_buckets(data, threshold):
"""
Return a downsampled version of data.
Parameters
----------
data: list of lists/tuples
data must be formated this way: [[x,y], [x,y], [x,y], ...]
or: [(x,y), (x,y), (x,y), ...]
threshold: int
threshold must be >= 2 and <= to the len of data
Returns
-------
data, but downsampled using threshold
"""
# Check if data and threshold are valid
if not isinstance(data, list):
raise LttbException("data is not a list")
if not isinstance(threshold, int) or threshold <= 2 or threshold >= len(data):
raise LttbException("threshold not well defined")
for i in data:
if not isinstance(i, (list, tuple)) or len(i) != 2:
raise LttbException("datapoints are not lists or tuples")
# Bucket size. Leave room for start and end data points
every = (len(data) - 2) / (threshold - 2)
a = 0 # Initially a is the first point in the triangle
next_a = 0
max_area_point = (0, 0)
sampled = [data[0]] # Always add the first point
for i in range(0, threshold - 2):
# Calculate point average for next bucket (containing c)
avg_x = 0
avg_y = 0
avg_range_start = int(math.floor((i + 1) * every) + 1)
avg_range_end = int(math.floor((i + 2) * every) + 1)
avg_rang_end = avg_range_end if avg_range_end < len(data) else len(data)
avg_range_length = avg_rang_end - avg_range_start
while avg_range_start < avg_rang_end:
avg_x += data[avg_range_start][0]
avg_y += data[avg_range_start][1]
avg_range_start += 1
avg_x /= avg_range_length
avg_y /= avg_range_length
# Get the range for this bucket
range_offs = int(math.floor((i + 0) * every) + 1)
range_to = int(math.floor((i + 1) * every) + 1)
# Point a
point_ax = data[a][0]
point_ay = data[a][1]
max_area = -1
while range_offs < range_to:
# Calculate triangle area over three buckets
area = math.fabs(
(point_ax - avg_x)
* (data[range_offs][1] - point_ay)
- (point_ax - data[range_offs][0])
* (avg_y - point_ay)
) * 0.5
if area > max_area:
max_area = area
max_area_point = data[range_offs]
next_a = range_offs # Next a is this b
range_offs += 1
sampled.append(max_area_point) # Pick this point from the bucket
a = next_a # This a is the next a (chosen b)
sampled.append(data[len(data) - 1]) # Always add last
return sampled