Question Summary
I have tried to troubleshoot this python ZigZag indicator but have not resolved the issue highlighted below and would appreciate any help with the logic of this function.
Details
The following code excerpt is from the Python zigzag indicator for candlestick charts. I have copied a minimal version of the code directly below to highlight where the logic is implemented. As per the chart below the indicator is not detecting a new peak at 2020-05-28 which should replace the peak at 2020-05-21
if down_thresh > 0:
raise ValueError('The down_thresh must be negative.')
initial_pivot = _identify_initial_pivot(close, up_thresh, down_thresh)
t_n = len(close)
pivots = np.zeros(t_n, dtype='i1')
pivots[0] = initial_pivot
# Adding one to the relative change thresholds saves operations. Instead
# of computing relative change at each point as x_j / x_i - 1, it is
# computed as x_j / x_1. Then, this value is compared to the threshold + 1.
# This saves (t_n - 1) subtractions.
up_thresh += 1
down_thresh += 1
trend = -initial_pivot
last_pivot_t = 0
last_pivot_x = close[0]
for t in range(1, len(close)):
if trend == -1:
x = low[t]
r = x / last_pivot_x
if r >= up_thresh:
pivots[last_pivot_t] = trend#
trend = 1
#last_pivot_x = x
last_pivot_x = high[t]
last_pivot_t = t
elif x < last_pivot_x:
last_pivot_x = x
last_pivot_t = t
else:
x = high[t]
r = x / last_pivot_x
if r <= down_thresh:
pivots[last_pivot_t] = trend
trend = -1
#last_pivot_x = x
last_pivot_x = low[t]
last_pivot_t = t
elif x > last_pivot_x:
last_pivot_x = x
last_pivot_t = t
if last_pivot_t == t_n-1:
pivots[last_pivot_t] = trend
elif pivots[t_n-1] == 0:
pivots[t_n-1] = trend
Code to reproduce this example
The following code will provide the output shown in the image (Numpy seed value included) and the dataframe does not require any additional file be downloaded. Copy this into a Jupyter notebook to see the exact same output. The actual logic is in the smaller code example above.
import pandas as pd
import numpy as np
import plotly.graph_objects as go
def genMockDataFrame(days,startPrice,colName,startDate,seed=None):
periods = days*24
np.random.seed(seed)
steps = np.random.normal(loc=0, scale=0.0018, size=periods)
steps[0]=0
P = startPrice+np.cumsum(steps)
P = [round(i,4) for i in P]
fxDF = pd.DataFrame({
'ticker':np.repeat( [colName], periods ),
'date':np.tile( pd.date_range(startDate, periods=periods, freq='H'), 1 ),
'price':(P)})
fxDF.index = pd.to_datetime(fxDF.date)
fxDF = fxDF.price.resample('D').ohlc()
fxDF.columns = [i.title() for i in fxDF.columns]
return fxDF
df = genMockDataFrame(100,1.1904,'eurusd','19/3/2020',seed=200)
PEAK, VALLEY = 1, -1
def _identify_initial_pivot(X, up_thresh, down_thresh):
"""Quickly identify the X[0] as a peak or valley."""
x_0 = X[0]
max_x = x_0
max_t = 0
min_x = x_0
min_t = 0
up_thresh += 1
down_thresh += 1
for t in range(1, len(X)):
x_t = X[t]
if x_t / min_x >= up_thresh:
return VALLEY if min_t == 0 else PEAK
if x_t / max_x <= down_thresh:
return PEAK if max_t == 0 else VALLEY
if x_t > max_x:
max_x = x_t
max_t = t
if x_t < min_x:
min_x = x_t
min_t = t
t_n = len(X)-1
return VALLEY if x_0 < X[t_n] else PEAK
def peak_valley_pivots_candlestick(close, high, low, up_thresh, down_thresh):
"""
Finds the peaks and valleys of a series of HLC (open is not necessary).
TR: This is modified peak_valley_pivots function in order to find peaks and valleys for OHLC.
Parameters
----------
close : This is series with closes prices.
high : This is series with highs prices.
low : This is series with lows prices.
up_thresh : The minimum relative change necessary to define a peak.
down_thesh : The minimum relative change necessary to define a valley.
Returns
-------
an array with 0 indicating no pivot and -1 and 1 indicating valley and peak
respectively
Using Pandas
------------
For the most part, close, high and low may be a pandas series. However, the index must
either be [0,n) or a DateTimeIndex. Why? This function does X[t] to access
each element where t is in [0,n).
The First and Last Elements
---------------------------
The first and last elements are guaranteed to be annotated as peak or
valley even if the segments formed do not have the necessary relative
changes. This is a tradeoff between technical correctness and the
propensity to make mistakes in data analysis. The possible mistake is
ignoring data outside the fully realized segments, which may bias analysis.
"""
if down_thresh > 0:
raise ValueError('The down_thresh must be negative.')
initial_pivot = _identify_initial_pivot(close, up_thresh, down_thresh)
t_n = len(close)
pivots = np.zeros(t_n, dtype='i1')
pivots[0] = initial_pivot
# Adding one to the relative change thresholds saves operations. Instead
# of computing relative change at each point as x_j / x_i - 1, it is
# computed as x_j / x_1. Then, this value is compared to the threshold + 1.
# This saves (t_n - 1) subtractions.
up_thresh += 1
down_thresh += 1
trend = -initial_pivot
last_pivot_t = 0
last_pivot_x = close[0]
for t in range(1, len(close)):
if trend == -1:
x = low[t]
r = x / last_pivot_x
if r >= up_thresh:
pivots[last_pivot_t] = trend#
trend = 1
#last_pivot_x = x
last_pivot_x = high[t]
last_pivot_t = t
elif x < last_pivot_x:
last_pivot_x = x
last_pivot_t = t
else:
x = high[t]
r = x / last_pivot_x
if r <= down_thresh:
pivots[last_pivot_t] = trend
trend = -1
#last_pivot_x = x
last_pivot_x = low[t]
last_pivot_t = t
elif x > last_pivot_x:
last_pivot_x = x
last_pivot_t = t
if last_pivot_t == t_n-1:
pivots[last_pivot_t] = trend
elif pivots[t_n-1] == 0:
pivots[t_n-1] = trend
return pivots
df = df["2020-04-28":"2020-06-20"]
pivots = peak_valley_pivots_candlestick(df.Close, df.High, df.Low ,.01,-.01)
df['Pivots'] = pivots
df['Pivot Price'] = np.nan # This line clears old pivot prices
df.loc[df['Pivots'] == 1, 'Pivot Price'] = df.High
df.loc[df['Pivots'] == -1, 'Pivot Price'] = df.Low
df["Date"] = df.index
fig = go.Figure(data=[go.Candlestick(x=df['Date'],
open=df['Open'],
high=df['High'],
low=df['Low'],
close=df['Close'])])
df_diff = df['Pivot Price'].dropna().diff().copy()
fig.add_trace(
go.Scatter(mode = "lines+markers",
x=df['Date'],
y=df["Pivot Price"]
))
fig.update_layout(
autosize=False,
width=1000,
height=800,)
fig.add_trace(go.Scatter(x=df['Date'],
y=df['Pivot Price'].interpolate(),
mode = 'lines',
line = dict(color='black')))
def annot(value):
if np.isnan(value):
return ''
else:
return value
j = 0
for i, p in enumerate(df['Pivot Price']):
if not np.isnan(p):
fig.add_annotation(dict(font=dict(color='rgba(0,0,200,0.8)',size=12),
x=df['Date'].iloc[i],
y=p,
showarrow=False,
text=annot(round(abs(df_diff.iloc[j]),3)),
textangle=0,
xanchor='right',
xref="x",
yref="y"))
j = j + 1
fig.update_xaxes(type='category')
fig.show()
For further reference there was also a similar question here.
