在Matplotlib中的条形图上显示负值的问题

Question

I am trying to create a bar chart with both positive and negative values using Matplotlib and experiencing difficulty in getting the negative values to show on Y axis. When the code is run, it'll correctly display all positive values (marked in red color) but the negative ones are not showing at all. Instead I'm getting a duplication of the positive values for the string marked "y1". Please see Image 1 attached and my code below.

The code I've used is:

import pandas as pd 
import numpy as np 
import matplotlib.pyplot as plt 
from matplotlib.pyplot import figure

data = pd.read_csv("C:\samplefile.csv")
fig = plt.figure()
figure(figsize = (22,3))
ax = plt.subplot(111)
x = data['Timing Event']
y = data['Diff Latency'].diff(periods = 1) > 0
y1 = data['Diff Latency'].diff(periods = 1) < 0
y_pos = np.arange(len(x))
plt.bar(y_pos, y, color=(1.0, 0, 0, 0.7))
plt.bar(y_pos, y1, color=(0, 0.6, 0, 0.7))

plt.tight_layout()
plt.show()

The dataset has 2 columns Timing Event in numbers eg.(0,1,2,3....) and used as index and "Diff Latency" which has both negative and positive values. Sample dataset is attached below:

Timing Event    Diff Latency
     0               -4
     1                3
     2                1
     3               -1
     4                2

Answer 1

If you just want to plot the positive and negative values in different colored bars, you can directly use pandas plotting based on the approach shown here

import pandas as pd
import matplotlib.pyplot as plt 

fig, ax = plt.subplots()

data = pd.DataFrame({'Timing_Event':[0,1,2,3,4], 'Diff_Latency':[-4, 3, 1, -1, 2]})
data['sign'] = data['Diff_Latency'] > 0

data['Diff_Latency'].plot(kind='bar', color=data.sign.map({True: (1.0, 0, 0, 0.7), False: (0, 0.6, 0, 0.7)}), 
                      ax=ax)
ax.axhline(0, color='k')