Drawing average line in histogram (matplotlib)
Question:
I am drawing a histogram using matplotlib in python, and would like to draw a line representing the average of the dataset, overlaid on the histogram as a dotted line (or maybe some other color would do too). Any ideas on how to draw a line overlaid on the histogram?
I am using the plot() command, but not sure how to draw a vertical line (i.e. what value should I give for the y-axis?
thanks!
Answers:
I would look at the largest value in your data set (i.e. the histogram bin values) multiply that value by a number greater than 1 (say 1.5) and use that to define the y axis value. This way it will appear above your histogram regardless of the values within the histogram.
You can use plot or vlines to draw a vertical line, but to draw a vertical line from the bottom to the top of the y axis, axvline is the probably the simplest function to use. Here’s an example:
In [80]: import numpy as np
In [81]: import matplotlib.pyplot as plt
In [82]: np.random.seed(6789)
In [83]: x = np.random.gamma(4, 0.5, 1000)
In [84]: result = plt.hist(x, bins=20, color='c', edgecolor='k', alpha=0.65)
In [85]: plt.axvline(x.mean(), color='k', linestyle='dashed', linewidth=1)
Out[85]: <matplotlib.lines.Line2D at 0x119758828>
Result:
This is old topic and minor addition, but one thing I have often liked is to also plot mean value beside the line:
import numpy as np
import matplotlib.pyplot as plt
np.random.seed(6789)
x = np.random.gamma(4, 0.5, 1000)
result = plt.hist(x, bins=20, color='c', edgecolor='k', alpha=0.65)
plt.axvline(x.mean(), color='k', linestyle='dashed', linewidth=1)
min_ylim, max_ylim = plt.ylim()
plt.text(x.mean()*1.1, max_ylim*0.9, 'Mean: {:.2f}'.format(x.mean()))
Which produces following result:
I am drawing a histogram using matplotlib in python, and would like to draw a line representing the average of the dataset, overlaid on the histogram as a dotted line (or maybe some other color would do too). Any ideas on how to draw a line overlaid on the histogram?
I am using the plot() command, but not sure how to draw a vertical line (i.e. what value should I give for the y-axis?
thanks!
I would look at the largest value in your data set (i.e. the histogram bin values) multiply that value by a number greater than 1 (say 1.5) and use that to define the y axis value. This way it will appear above your histogram regardless of the values within the histogram.
You can use plot or vlines to draw a vertical line, but to draw a vertical line from the bottom to the top of the y axis, axvline is the probably the simplest function to use. Here’s an example:
In [80]: import numpy as np
In [81]: import matplotlib.pyplot as plt
In [82]: np.random.seed(6789)
In [83]: x = np.random.gamma(4, 0.5, 1000)
In [84]: result = plt.hist(x, bins=20, color='c', edgecolor='k', alpha=0.65)
In [85]: plt.axvline(x.mean(), color='k', linestyle='dashed', linewidth=1)
Out[85]: <matplotlib.lines.Line2D at 0x119758828>
Result:
This is old topic and minor addition, but one thing I have often liked is to also plot mean value beside the line:
import numpy as np
import matplotlib.pyplot as plt
np.random.seed(6789)
x = np.random.gamma(4, 0.5, 1000)
result = plt.hist(x, bins=20, color='c', edgecolor='k', alpha=0.65)
plt.axvline(x.mean(), color='k', linestyle='dashed', linewidth=1)
min_ylim, max_ylim = plt.ylim()
plt.text(x.mean()*1.1, max_ylim*0.9, 'Mean: {:.2f}'.format(x.mean()))
Which produces following result: