How to draw pandas dataframe using Matplotlib hist with multiple y axes-CodePudding

I have a dataframe as below:

frame_id time_stamp    pixels  step
0        50   06:34:10  0.000000       0
1       100   06:38:20  0.000000       0
2       150   06:42:30  3.770903       1
3       200   06:46:40  3.312285       1
4       250   06:50:50  3.077356       0
5       300   06:55:00  2.862603       0

I want to draw two y-axes in one plot. One is for pixels. The other is for step. x-axis is time_stamp. I want the plot for step like the green line like this:

CodePudding user response：

Here's an example that could help. Change d1 and d2 as per your variables and the respective labels as well.

import numpy as np                   
import matplotlib.pyplot as plt      

rng = np.random.default_rng(seed=0)

d1 = rng.normal(loc=20, scale=5, size=200)
d2 = rng.normal(loc=30, scale=5, size=500)

fig, ax1 = plt.subplots(figsize=(9,5))

#create twin axes
ax2 = ax1.twinx()

ax1.hist([d1], bins=15, histtype='barstacked', linewidth=2,
        alpha=0.7)
ax2.hist([d2], bins=15, histtype='step', linewidth=2,
        alpha=0.7)

ax1.set_xlabel('Interval')
ax1.set_ylabel('d1 freq')
ax2.set_ylabel('d2 freq')

plt.show()

Histogram

Getting the bar labels is not easy with the two types of histograms in the same plot using matplotlib.

bar_labels

CodePudding user response：

Instead of histograms you could use bar plots to get the desired output. I have also added in a function to help get the bar labels.

import matplotlib.pyplot as plt
import numpy as np
time = ['06:34:10','06:38:20','06:42:30','06:46:40','06:50:50','06:55:00']

step = [0,0,1,1,0,0]
pixl = [0.00,0.00,3.77,3.31,3.077,2.862]

#function to add labels
def addlabels(x,y):
    for i in range(len(x)):
        plt.text(i, y[i], y[i], ha = 'center')
fig, ax1 = plt.subplots(figsize=(9,5))

#generate twin axes
ax2 = ax1.twinx()

ax1.step(time,step, 'k',where="mid",linewidth=1)

ax2.bar(time,pixl,linewidth=1)

addlabels(time,step)
addlabels(time,pixl)
ax1.set_xlabel('Time')
ax1.set_ylabel('Step')
ax2.set_ylabel('Pixels')

plt.show()

bar_plot