matplotlib mean interval plot

Question

I'm transitioning from R to python, and was looking to plot the mean line of a two variables. It is the plot of the x variable is split into intervals for the x axis, and mean of the y variable for the y axis.

For example, if I have 1000 points (x1,y1) to (x1000, y1000), and want to plot into 3 bins, I would have 3 bars of x intervals where each would have the mean of the y variables that fall into that respective interval.

Does anyone know what this plot is called, and how I can do this in python? In R, I use the "cut" command and then plot the x,y of the cut.

Thanks!

Jianxun Li · Accepted Answer · 2015-06-18 08:19:43Z

2

For the follow-up questions, we can do something more powerful using boxplot.

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

# simulate some artificial data
x = np.random.randn(1000,)
y = 5 * x ** 2 + np.random.randn(1000,)
data = pd.DataFrame(0.0, columns=['X', 'Y'], index=np.arange(1000))
data.X = x
data.Y = y

# now do your stuff
# ================================
# use the pandas 'cut' function
data['X_bins'] = pd.cut(data.X, 3)
data.set_index('X_bins', append=True, inplace=True)
data.drop('X', axis=1, inplace=True)
data.unstack(level=1).boxplot()

enter image description here

answered Jun 18, 2015 at 8:19

Jianxun Li

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Jianxun Li · Accepted Answer · 2015-06-17 19:15:50Z

1

Here is an example to do it.

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

# simulate some artificial data
x = np.random.randn(1000,)
y = 5 * x ** 2 + np.random.randn(1000,)
data = pd.DataFrame(0.0, columns=['X', 'Y'], index=np.arange(1000))
data.X = x
data.Y = y

# now do your stuff
# ================================
# use the pandas 'cut' function
data['X_bins'] = pd.cut(data.X, 3)
# for each bin, calculate the mean of Y
result = data.groupby('X_bins')['Y'].mean()
# do the plot
result.plot()

enter image description here

answered Jun 17, 2015 at 19:15

Jianxun Li

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1 Comment

curious_programmer Over a year ago

awesome, this is exactly what I was looking for--thanks! A bit of a stretch here, but do you know how to plot error bars for the points as well?

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