Mathplotlib graph problems

user_17817899 0
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I'm trying to display data from a weather station with mathplotlib. For some reason that I can't quite figure out my last values on the graph are acting randomly, going back in time on the x axis.

x axis is the dates,

y axis is the water level

y1 axis is the discharge flow

Here's a picture of the result Graph

import pandas as pd
import matplotlib.pyplot as plt

url_hourly = "https://dd.weather.gc.ca/hydrometric/csv/BC/hourly/BC_08MG005_hourly_hydrometric.csv"
url_daily  = "https://dd.weather.gc.ca/hydrometric/csv/BC/daily/BC_08MG005_daily_hydrometric.csv"
fields = ["Date","Water Level / Niveau d'eau (m)", "Discharge / Débit (cms)"]

#Read csv files  
hourly_data = pd.read_csv(url_hourly, usecols=fields)
day_data = pd.read_csv(url_daily, usecols=fields)

#Merge csv files
water_data = pd.concat([day_data,hourly_data])

#Convert date to datetime
water_data['Date'] = pd.to_datetime(water_data['Date']).dt.normalize()
water_data['Date'] = water_data['Date'].dt.strftime('%m/%d/%Y')

# CSV files contains 288 data entries per day (12per hour * 24hrs). Selecting every 288th element to represent one day
data_24hr = water_data[::288]

# Assigning columns to x, y, y1 axis
x = data_24hr[fields[0]]
y1 = data_24hr[fields[1]]
y2= data_24hr[fields[2]]

#Ploting the graph
fig, ax1 = plt.subplots()
ax2 = ax1.twinx()
curve1 = ax1.plot(x,y1, label='Water Level', color = 'r', marker="o")
curve2 = ax2.plot(x,y2,label='Discharge Volume', color = 'b',marker="o")
plt.plot()
plt.show()

Any tips would be greatly appreciated as I'm quite new to this

thank you

graph python
1 Answers

Okay I went through the code removed the duplicates (as suggest by Arne) by the "Date" column. Oh and I made the graph formatting slightly more readable. This graphed without going back in time:

import pandas as pd
import matplotlib.pyplot as plt
from matplotlib import ticker

url_hourly = "https://dd.weather.gc.ca/hydrometric/csv/BC/hourly/BC_08MG005_hourly_hydrometric.csv"
url_daily  = "https://dd.weather.gc.ca/hydrometric/csv/BC/daily/BC_08MG005_daily_hydrometric.csv"
fields = ["Date","Water Level / Niveau d'eau (m)", "Discharge / Débit (cms)"]

#Read csv files  
hourly_data = pd.read_csv(url_hourly, usecols=fields)
day_data = pd.read_csv(url_daily, usecols=fields)

#Merge csv files
water_data = pd.concat([day_data,hourly_data])

#Convert date to datetime
water_data['Date'] = pd.to_datetime(water_data['Date']).dt.normalize()
water_data['Date'] = water_data['Date'].dt.strftime('%m/%d/%Y')
# CSV files contains 288 data entries per day (12per hour * 24hrs). Selecting every 288th element to represent one day
data_24hr = water_data.iloc[::288]
data_24hr.drop_duplicates(subset="Date",inplace=True) #remove duplicates according to the date column
# Assigning columns to x, y, y1 axis
x = data_24hr[fields[0]]
y1 = data_24hr[fields[1]]
y2= data_24hr[fields[2]]

print(len(x), len(y1))
#Ploting the graph
fig, ax1 = plt.subplots()
ax2 = plt.twinx()
curve1 = ax1.plot(x, y1, label='Water Level', color = 'r', marker="o")
curve2 = ax2.plot(x, y2, label='Discharge Volume', color = 'b',marker="o")
fig.autofmt_xdate(rotation=90)
plt.show()

user_116094620
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