Plotting line graph for 3 variables in python

Question

Country Month   GDPA
USA     January  5
USA     February 10
USA     March    5
Canada  January  7
Canada  February 4
Canada  March    10
Mexico  January  9
Mexico  February 17
Mexico  March    8

Above is my data frame.

I want to make a line graph of the df. Where the x axis is the variable Month. The y axis is GDPA. And there are three separate lines for each country. Preferably using matplotlib only.

plt.plot(df[‘Country’], df[‘GDPA’], df[‘Month’]

My code above does not produce the expected graph because the lines are connected and it doesn’t even take the GDPA values into account.

I want it so that the x axis is: January February March
y axis is GDPA values.
and there are 3 lines (for each country)

Can you include a picture of what graph you are getting with your code above? — Aaron Jones
– Aaron Jones, Commented Nov 22, 2020 at 0:16

Sash Sinha · Accepted Answer · 2020-11-22 01:14:41Z

4

This may not be as elegant as possible, but a low-level way to do it is to basically just make a set of the countries (so you have no duplicates), then loop over that set and plot a line for each country.

import matplotlib.pyplot as plt
import pandas

d = {'Country': ['USA', 'USA', 'USA', 'Canada', 'Canada', 'Canada', 'Mexico', 'Mexico', 'Mexico'],
     'Month': ['January', 'February', 'March', 'January', 'February', 'March', 'January', 'February', 'March'],
     'GDPA': [5, 10, 5, 7, 4, 10, 9, 17, 8]}
df = pandas.DataFrame(data=d)
print(df)

country_set = set(df['Country'])

plt.figure()
for country in country_set:
     selected_data = df.loc[df['Country'] == country]
     plt.plot(selected_data['Month'], selected_data['GDPA'], label=country)
     
plt.legend()
plt.show()

Pure python and matplotlib!

edited Nov 22, 2020 at 1:14

Sash Sinha

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answered Nov 22, 2020 at 1:13

chrisp

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4 Comments

gboffi Over a year ago

I don't understand if the sequence of the months is correct by chance (possibly because of a particular order of items in the data frame) or it's correct because it must be necessarily so (possibly because Matplotlib recognizes the months' names and order them accordingly to calendar)

chrisp Over a year ago

I believe they just match the order of the data frame. To matplotlib, they are just strings. A more robust code would sort on the months before calling plot().

gboffi Over a year ago

I appreciate your reply

gboffi Over a year ago

① calendar = ('January', 'February', 'March', ...) ② def ordered_by_month(months, values):return zip(*sorted(zip(months, values), key=lambda t:calendar.index(t[0]))) ③ plt.plot(*ordered_by_month(months, GDPA), label=country)

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