I have a captured a data from a displacement sensor, the delta values for one iteration look like this. 0, 1, 2, 4, 7, 9, 14, 24, 14, 10, 9, 7, 3 2, 1, 0, 0, 0, 0, -1, -3, -5, -7, -9, -14, -24, -14, -9, -8, -6, -4, -3, -1, 0, 0, 0. (other iterations are also have same pattern.)
I am interested in the maxima and minima points of a curves. I start with a initial position and come back to this position for a loops for line(I've take the partial sum of the values to get the total displacement or line). The partial sum look like this [0, 1, 3, 7, 14, 23, 37, 61, 75, 85, 94, 101, 104, 106, 107, 107, 107, 107, 107, 106, 103, 98, 91, 82, 68, 44, 30, 21, 13, 7, 3, 0, -1, -1, -1, -1]. I am interested in 107 and -1 (the next curve minima)
But I am not figure out the code for say n no. of curve (iteration). Can you help me with this?
You can use this function for getting the absolute extrema:
def extrema(value, deltas):
max_value = min_value = value
for delta in deltas:
value += delta
if value < min_value:
min_value = value
elif value > max_value:
max_value = value
return min_value, max_value
Here I have adapted the function to yield local extrema:
def extrema(value, deltas):
values = [value]
for delta in deltas:
value += delta
values.append(value)
average = sum(values)/len(values)
threshold = (max(values) - min(values))/6
min_threshold = average - threshold
max_threshold = average + threshold
min_value = max_value = None
for value in values:
if value < min_threshold:
if min_value is None or value < min_value:
min_value = value
elif value > max_threshold:
if max_value is None or value > max_value:
max_value = value
elif min_value is not None and max_value is not None:
yield min_value, max_value
max_value = min_value = None
You can fine-tune the function from here. For instance, the function could skip the first values until min_threshold < value < max_threshold to find the start of a cycle, and at the end it could yield the last extremum if it did not end with a full cycle.
Lastly, here is a function that works with point tuples as in your example data.
class Point(object):
__slots__ = ('x', 'y')
def __init__(self, x=0, y=0):
self.x = x
self.y = y
def __repr__(self):
return str((self.x, self.y))
def __iadd__(self, other):
self.x += other.x
self.y += other.y
return self
def __isub__(self, other):
self.x -= other.x
self.y -= other.y
return self
def __idiv__(self, number):
self.x /= number
self.y /= number
return self
def abs(self):
return abs(self.x) + abs(self.y)
def copy(self):
return Point(self.x, self.y)
def extrema(moves, jitter=0.1, threshold=1000, sample=16):
point = Point()
minpoint = Point()
maxpoint = Point()
average = Point()
average /= 1.0
turned = False
for move in moves:
point += move
x = point.x
if x < minpoint.x:
minpoint.x = x
elif x > maxpoint.x:
maxpoint.x = x
y = point.y
if y < minpoint.y:
minpoint.y = y
elif y > maxpoint.y:
maxpoint.y = y
delta = move.copy()
delta -= average
delta /= sample
average += delta
if average.abs() < jitter:
if point.abs() > threshold:
turned = True
elif turned:
yield minpoint, maxpoint
point = Point() # reset (calibrate)
minpoint = Point()
maxpoint = Point()
turned = False
# read data from file
moves = [Point(*map(int, move.split(',')))
for move in open('data.txt').read().split(';') if move]
# generate extrema
print list(extrema(moves))