Plotting values versus strings in matplotlib?

Question

I am trying to create a plot in matplotlib where the x-values are integers and the y-values are strings. Is it possible to plot data of this type in matplotlib? I examined the documentation and the gallery for matplotlib and could not find any examples of this type.

I have many lists bound to a variable called my_lists. The structure looks like this:

mylists = [765340, 765371, 765310,'MA011',],
          [65310, 'MA015'],
          [765422, 765422, 24920205, 24920161, 'MA125'],
          [765422, 'MA105'], 
          [765371, 12345, 'MA004']

In each list, all items except the last item are x-values. The last item in each list is a string, which is the single y-value. How can I plot this is matplotlib? Here was my attempt:

import matplotlib.pyplot as plt

for sub_list in my_lists:
    x_value = sub_list[:1]
    y_value = sub_list[-1]
    plt.plot(x_value, y_value, "ro")
    plt.show()

The above code throws me this error:

ValueError: could not convert string to float: MA011

How can integers versus strings be plotted?

GWW · Accepted Answer · 2011-08-19 17:14:51Z

2

You could probably do something like this, where you give each y "string" a unique index value. You may have to fiddle with the spacing for i. Ie. i*2 instead of i to make things look nice. After that you set the tick label for each of those indexes to its corresponding string.

import matplotlib.pyplot as plt

fig = plt.figure(figsize=(9,7))
ax1 = fig.add_subplot(111)


mylists = [[765340, 765371, 765310,'MA011',], [65310, 'MA015'], 
           [765422, 765422, 24920205, 24920161, 'MA125'],
           [765422, 'MA105'],[765371, 12345, 'MA004']]

x = []
y = []
y_labels = []
y_ticks = []
for i,sub_list in enumerate(mylists):
    y_labels.append(sub_list[-1])
    y_ticks.append(i)
    for v in sub_list[:-1]:
        x.append(v)
        y.append(i)

ax1.set_yticks(y_ticks)
ax1.set_yticklabels(y_labels)
ax1.plot(x, y, "ro")
plt.show()

EDIT:

Sorry I forgot to include the enuemrate call in the for loop. It basically sets the value of i to the index of the current sub_list. Then you use the index instead of the string value as the y-value. After that you replace the label for those y-values with the actual string value.

edited Aug 19, 2011 at 17:14

answered Aug 19, 2011 at 15:15

GWW

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4 Comments

drbunsen Over a year ago

Thanks for the help. The code you provided seems to throw some errors, and I'm not entirely sure what the for loop is doing. Could you possibly explain your solution a bit further? Thanks.

GWW Over a year ago

@dr.bunsen: Sorry I had a typo in the code I fixed it in my edit.

drbunsen Over a year ago

Fantastic! This worked perfectly. I now understand how you used enumerate() to build the y-axis and then added the strings as y_labels. Thanks again, your help is greatly appreciated!

GWW Over a year ago

@dr.brunsen: No problem, I'm glad it helped. As a side note I noticed another typo in your original code, you actually want sub_list[:-1] to loop through all but the last element.

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