Day 12 - Task planning & visualization

Date: October 5, 2026

⚠️Homework

Homework 4 due October 11, 2026

‼️Ending Skills

Last week for skills: 0

🆕New Skills

First week for skills: 2

Skills: None

Pre-reading: 4.2.2, 4.2.3, 4.2.4, 4.2.5, 4.2.6

Supplementary Videos

Task Planning and Visualization

Intro (25 mins)

Often, what you want to do is big enough that jumping right into code is a mistake.
Instead, it's a good idea to develop a task plan -- as text, pictures, etc.
A plan has concrete inputs & outputs, notes about what functions you might use, and a concrete sequence of steps and how the data is transformed through them.
You might repeat this process at a smaller level if one of the steps still seems complex.

Example: Task plan to analyze weather data

Let's say we had the following table of weather data:

weather-data =
  table: date, temperature, precipitation
    row: "2025-01-01", 62, 0.1
    row: "2025-01-02", "45", 3
    row: "2025-01-03", 28, 0.2
    row: "2025-01-04", 55, -1
    row: "2025-01-05", 90, 0
  end

And we wanted to visualize the number of cold, mild, and hot days.

The output is going to be a chart, which has bars for counts of cold, mild, and hot days. Let's say cold is below 40F, mild is 40F to 60F, and hot is above 60F.
Our task plan, the steps we need to do are:
1. Normalize the data -- in particular, the temperature column needs to be all numbers! While the precipitation column seems to have problems (a negative number), since our task doesn't have anything to do with precipitation, we don't need to deal with that.
2. Create a new column with the three different bins -- cold, mild, or hot.
3. Chart that new column.

For the first step, we can use is-string and string-to-number-unsafe to convert the errant values. First, let's define a helper that does the conversion:

fun normalize-temp(v) -> Number:
  doc: "given a number or a string that represents a number, converts to a number"
  if is-string(v): 
    string-to-number-unsafe(v)
  else: 
    v
  end
where:
  normalize-temp(10) is 10
  normalize-temp("13") is 13
end

string-to-number-unsafe converts to a number if possible, and errors if not! Since we only use it on strings that contain numbers, this will always work. If we wanted to use it on strings that did contain numbers, we could use string-to-number-default(N) -- this function takes a default, and returns a function that can be applied -- i.e., string-to-number-default(0)("hello") will return 0, vs string-to-number-default(0)("100") returns 100.

Then we can use that to transform the column:
```
fixed-data = transform-column(weather-data, "temperature", normalize-temp)
```

For the second step, we can define a helper function that does the bucket conversion:

fun bucket-temp(t :: Number) -> String:
  doc: "numbers < 40 turn into 'cold', >=40 and < 60 to 'mild' and >=60 to 'hot'"
  if t < 40:
    "cold"
  else if t < 60:
    "mild"
  else:
    "hot"
  end
where:
  bucket-temp(-10) is "cold"
  bucket-temp(0) is "cold"
  bucket-temp(39.9) is "cold"
  bucket-temp(40) is "mild"
  bucket-temp(58) is "mild"
  bucket-temp(60) is "hot"
  bucket-temp(100) is "hot"
end

Now we can use that to add a new column:

with-buckets = build-column(fixed-data, "temp-category", lam(r :: Row) -> String: bucket-temp(get-column(r, "temperature")) end)

Note how I made my helper function bucket-temp just take a number, so it was easy to test, and then used a lam to pass a Row -> String function to build-column, which handled extracting the column value and passing it to the helper. I could have had bucket-temp take in a Row, but it would have made testing more complex.

Now, our third and final step in our task plan is to visualize the results. We can do this with freq-bar-chart:
```
freq-bar-chart(with-buckets, "temp-category")
```

Class Activity (30 mins)

Using the same data, visualize the number of days that were "dry" (no rain), "drizzly" (< 1" of rain), and "wet" (>= 1" of rain). It's up to you to decide how to handle the bad data! Think about what it might represent! First, make a plan!
Consider you have the following table:

employees =
  table: full-name :: String, department :: String
    row: "Jordan Smith", "Sales"
    row: "Alexandra Lee", "Engineering"
    row: "Sam", "Marketing"
    row: "Ng, Alice", "Operations"
  end

You want to have in your data, in addition to "full name", columns for given name (or first name) and family name (or last name). Make a plan for computing these two columns, thinking carefully about what different cases you might have to consider. Are all of the cases you thought of reflected in the example above? If not, add more examples to the data.

Wrap up (5 mins)

Planning is useful for all programming, and all good programmers do it -- probably, as you gain experience, simpler things you will plan only in your head, and more complex things you will plan on paper (or on whiteboards, etc). But the process of planning remains the same, whatever the scale!

Skills: None​

Pre-reading: 4.2.2, 4.2.3, 4.2.4, 4.2.5, 4.2.6​

Supplementary Videos​

Reference: For all work with tables, refer to the Tables page in the menu at the top of the page!​

Intro (25 mins)​

Example: Task plan to analyze weather data​

Class Activity (30 mins)​

Wrap up (5 mins)​