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Data Foundations · A little practice goes a long way.

← Wrangle / Preprocess lessonsTINY TABLES · REAL PYTHON · YOUR PACE
Types, dates & missingness · W17 · 8 MIN

Fill missing values

Choose and document an imputation rule.

Exercises within this concept

  1. FollowFollow the techniqueCurrent exercise
  2. ChangeAdapt a requirement
  3. TransferChoose and combine

Understand the idea

fillna replaces missing values only. The fill rule is an assumption, so choose it explicitly and retain evidence of the original gaps.

Concept sketch: fill only the gap with median 3rowpriceA2BNaNC4rowpriceA2B3C4fill only the gap with median 3
Illustration · not the exercise output

A small example

[2, missing, 6] filled with its observed median becomes [2, 4, 6]; the 4 is an estimate.

Follow the code

Apply the idea to the supplied table. Read from top to bottom; the final line displays the result.

df["tip"] = df["tip"].fillna(df["tip"].median())
df

What each part does

median()
middle observed value
fillna(value)
replace gaps only
Other choices for later exercises
mode().iloc[0]
first most-common value; ties need a decision

Your inputs

The editable setup on the right creates df. Run executes the setup and your work from top to bottom.

Messy café orders · 8 synthetic rows
orderdrinksizepricetipdate
101" latte "LARGE6.2012026-06-01
102TEAsmall3.100.52026-06-02
103" mocha "LARGEoopsNonenot a date
104LatteSmallNone0.82026-06-04
104LatteSmallNone0.82026-06-04
105"tea "SMALL4.200.62026-06-05
106ESPRESSOsmall2.500.22026-06-06
107" mocha"large6.801.52026-06-07

Your task · Follow

  1. Using df, fill missing tip with the observed median tip, keeping all rows.
  2. This is an exercise assumption, not proof of the true tip.
  3. Keep the changes in df and display it.
  4. Use: fillna().
Hint

Calculate the observed median before filling; do not replace known values.

Reveal solution

One way to do it. Keep any supplied setup in the editor and use this in the Your work section.

df["tip"] = df["tip"].fillna(df["tip"].median())
df
Your task · Follow
  1. Using df, fill missing tip with the observed median tip, keeping all rows.
  2. This is an exercise assumption, not proof of the true tip.
  3. Keep the changes in df and display it.
  4. Use: fillna().

Tab: indent · Shift+Tab: outdent · Esc, then Tab: leave editor

Edit Python. Control or Command plus Enter runs it. Tab indents by four spaces. Shift plus Tab outdents. Press Escape, then Tab or Shift plus Tab to leave the editor.

Each run executes all editor code in a fresh Python session. Display a value by leaving it on the final line.

Python starts when you open a lesson.

Output

Run your code to see what Python returns.