Changing what the ends of whiskers represent in matplotlib's boxplot function

Question

I understand that the ends of whiskers in matplotlib's box plot function extend to max value below 75% + 1.5 IQR and minimum value above 25% - 1.5 IQR. I would like to change it to represent max and minimum values of the data or the 5th and 95th quartile of the data. Is is possible to do this?

Answer 1

To get the whiskers to appear at the min and max of the data, set the whis parameter to an arbitrarily large number. In other words: boxplots = ax.boxplot(myData, whis=np.inf).

The whis kwarg is a scaling factor of the interquartile range. Whiskers are drawn to the outermost data points within whis * IQR away from the quartiles.

Now that v1.4 is out:

In matplotlib v1.4, you can say: boxplots = ax.boxplot(myData, whis=[5, 95]) to set the whiskers at the 5th and 95th percentiles. Similarly, you'll be able to say boxplots = ax.boxplot(myData, whis='range') to set the whiskers at the min and max.

Note: you could probably modify the artists contained in the boxplots dictionary returned by the ax.boxplot method, but that seems like a huge hassle

Answer 2

Set the boxplot option whisk=0 to hide the inbuilt whiskers. Then create the custom whiskers that show data from 5% to 95%.

#create markings that represent the ends of whiskers
low=data.quantile(0.05) 
high=data.quantile(0.95)
plt.scatter(range(1,len(low)+1),low,marker='_')
plt.scatter(range(1,len(low)+1),high,marker='_')
#connects low and high markers with a line
plt.vlines(range(1,len(low)+1),low,high)

That should create vertical lines with whisker markings behind the boxes at 5% at 95%.