Our task

Data

The file temperatures.csv (raw csv file) contains hourly air temperature measurements for the observation station “Vantaa Helsinki-Vantaan lentoasema” (Helsinki airport) during 2022.

Origin of the data

Data obtained from https://en.ilmatieteenlaitos.fi/download-observations#!/ on 2023-09-27.

Data has been provided by the Finnish Meteorological Institute under the Creative Commons Attribution 4.0 International license (CC BY 4.0): https://en.ilmatieteenlaitos.fi/open-data-licence

Our initial goal

Our initial goal for this exercise is to plot a series of temperatures for 25 measurements and to compute and plot the arithmetic mean. We imagine that we assemble a working script from various StackOverflow/ChatGPT recommendations and arrive at:

import pandas as pd
from matplotlib import pyplot as plt

num_measurements = 25

# read data from file
data = pd.read_csv("temperatures.csv", nrows=num_measurements)
temperatures = data["Air temperature (degC)"]

# compute statistics
mean = sum(temperatures) / num_measurements

# plot results
plt.plot(temperatures, "r-")
plt.axhline(y=mean, color="b", linestyle="--")
plt.show()
plt.savefig("25.png")
plt.clf()

This example is in Python but we will try to see “through” the code and focus on the bigger picture and hopefully manage to imagine other languages in its place. For the Python experts: we will not see the most elegant Python.

Further goals

  • Once we get this working for 25 measurements, our task changes to also plot the first 100 and the first 500 measurements in two additional plots.

  • Then we wish to generalize the code so that a user can compute and plot this for any number, without changing the code (with a command line interface).

How we plan to solve it

Before we attempt to do this, we discuss with workshop participants how they would tackle this problem.

Together we improve the code based on suggestions from learners towards more modularity and re-usability.

Instructor note

Participants give suggestions and ask questions via collaborative document and instructor(s) try to follow and answer. They can also roughly follow the ideas and steps in the An iterative solution.

It is OK and good if mistakes happen and it is fun if the instructor(s) can convey a bit of “improv” feel to this lesson.

Additional exercises

Draw a call tree for one of your recent projects. Identify the functions in your call tree which are “pure” (which have no side-effects).