Matplotlib 以一种非常奇怪的方式绘制图形

Question

正在尝试绘制一天中的紫外线指数。数据来自 api，经过一些处理后，它在一个很好的列表中为我提供了数据。然而，情节绝对令人作呕。 Link to graph。 Y 轴值重复并四处乱扔，所以有多个 0，多个 0 两边都是正数，解释起来简直就是一场噩梦。提前致谢

代码：

import requests
import re
from matplotlib import pyplot as plt
import numpy as np

# Get weather information
response = requests.get("https://api.openweathermap.org/data/2.5/onecall?lat=55.583328&lon=13.0&lang=se&exclude=minutely,daily,alerts&units=metric&appid=0f0212703cfecb4699dfc2c7edde950a")

# Save weather information to file
with open("weather.csv", 'w') as file:
    file.write(response.text)

# Opens the file and gets all the values of "uv-index"
with open("Weather.csv", 'r') as text:
    pattern = 'uvi":(.*?),'
    Line = text.read()
    substring = np.array(re.findall(pattern, Line))

# Creates an x-axis as a list with the same size as y-axis
# If they're not the same size, error is given:
# ValueError: x and y must have same first dimension, but have shapes (12,) and (49,)
x_axis = []
for i in range(len(substring)):
    x_axis.append(i)
x_axis = np.array(x_axis)

# Determines size and plots graph
fig, ax = plt.subplots(figsize=(10, 6))
ax.plot(x_axis, substring)

# Creates labels
plt.title("UV-Index today")
plt.xlabel("Time")
plt.ylabel("UV-Index")

# Saves the plot as image and shows it on screen
plt.savefig("UV-Index" + ".png")
plt.show()

Answer 1

您的 substring 是一个字符串列表。 Matplotlib 将字符串视为离散值（因此 '0' 和 '0.01' 以及 '0' 和 '1000' 之间的距离没有差异；并且它们之间没有顺序，因此 '1000' 可能看起来低于 '0'）。

在绘图之前将您的 substring 转换为浮点数：

substring = list(map(float,substring))

或者，由于您的子字符串是一个 numpy 数组：

substring = substring.astype('float')

Answer 2

如前所述，您的 Y 数据不是数字类型。

此外，这绝对是一种解析 json 响应的新方法。试试这个：

import json
s = json.loads(response.text)
df = pd.json_normalize(s['hourly'])
df['dt'] = pd.to_datetime(df['dt'], unit='s')
df.plot(x="dt", y='uvi')
# Creates labels
plt.title("UV-Index today")
plt.xlabel("Time")
plt.ylabel("UV-Index")
plt.show()

根据要求，完整示例。不确定为什么将结果保存到文本文件，但它是 json 文件而不是 csv 文件。

import requests
from matplotlib import pyplot as plt
import json
import pandas as pd
import numpy as np

# Get weather information
response = requests.get("https://api.openweathermap.org/data/2.5/onecall?lat=55.583328&lon=13.0&lang=se&exclude=minutely,daily,alerts&units=metric&appid=0f0212703cfecb4699dfc2c7edde950a")

# Save weather information to file
with open("weather.json", 'w') as file:
    file.write(response.text)

# Evaluate JSON string to JSON object
s = json.loads(response.text)

# Create DataFrame with hourly data
df = pd.json_normalize(s['hourly'])

# Convert time stamps to actual datetime values
df['dt'] = pd.to_datetime(df['dt'], unit='s')

# Determines size and plots graph
df.plot(x="dt", y='uvi', figsize=(10, 6))

# Creates labels
plt.title("UV-Index today")
plt.xlabel("Time")
plt.ylabel("UV-Index")

# Saves the plot as image and shows it on screen
plt.savefig("UV-Index" + ".png")
plt.show()

Answer 3

这解决了所有问题，并且代码不言自明，但请询问您是否对任何事情感到困惑：

import requests
import re
from matplotlib import pyplot as plt
import numpy as np
import json

response = requests.get("https://api.openweathermap.org/data/2.5/onecall?lat=55.583328&lon=13.0&lang=se&exclude=minutely,daily,alerts&units=metric&appid=0f0212703cfecb4699dfc2c7edde950a")

with open("weather.txt", 'w') as file:
    file.write(response.text)

# this converts the JSON as a string to JSON as a dictionary
dict1 = json.loads(response.text)

y_axis = []
for entry in dict1['hourly']:
    y_axis.append(entry['uvi'])

y_axis = np.array(y_axis)
x_axis = np.array(range(len(x_axis)))

fig, ax = plt.subplots(figsize=(10, 6))
ax.plot(x_axis, y_axis)

plt.title("UV-Index today")
plt.xlabel("Time (Hours)")
plt.ylabel("UV-Index")

plt.savefig("UV-Index" + ".png")
plt.show()

（另外，检查你的 weather.csv 文件；它不应该是 csv 格式，因为它是 json 数据，而不是 table 数据。）

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