Tuesday, November 22, 2011

Boxplots using matplotlib

If you ever need to graph anything using python, I recommend matplotlib. Here is an example of a boxplot below. The link will take you to the help documentation in matplotlib. It's pretty good compared to many other python modules.


from pylab import *

# fake up some data
spread= rand(50) * 100
center = ones(25) * 50
flier_high = rand(10) * 100 + 100
flier_low = rand(10) * -100
data =concatenate((spread, center, flier_high, flier_low), 0)

# basic plot
boxplot(data)
#savefig('box1')

# notched plot
figure()
boxplot(data,1)
#savefig('box2')

# change outlier point symbols
figure()
boxplot(data,0,'gD')
#savefig('box3')

# don't show outlier points
figure()
boxplot(data,0,'')
#savefig('box4')

# horizontal boxes
figure()
boxplot(data,0,'rs',0)
#savefig('box5')

# change whisker length
figure()
boxplot(data,0,'rs',0,0.75)
#savefig('box6')

# fake up some more data
spread= rand(50) * 100
center = ones(25) * 40
flier_high = rand(10) * 100 + 100
flier_low = rand(10) * -100
d2 = concatenate( (spread, center, flier_high, flier_low), 0 )
data.shape = (-1, 1)
d2.shape = (-1, 1)
#data = concatenate( (data, d2), 1 )
# Making a 2-D array only works if all the columns are the
# same length. If they are not, then use a list instead.
# This is actually more efficient because boxplot converts
# a 2-D array into a list of vectors internally anyway.
data = [data, d2, d2[::2,0]]
# multiple box plots on one figure
figure()
boxplot(data)
#savefig('box7')

show()


This will produce the following:
Pretty sweet.  Maybe you could use this to graph the elevation profile?  (Hint: you can)

Enjoy

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