The Data Analysis Process: From Question to Decision · Lesson 1 · 3 minutes

Fix messy data

Identify daily cleaning tasks

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  1. Lee's first day

    Lee starts his new job today at a bike rental shop. He expects to make shiny charts all day. Instead, his screen shows messy lists with missing dates and typos.

    Lee's first day. Lee starts his new job today at a bike rental shop. He expects to make shiny charts all day. Instead, his screen shows messy lists with missing dates and typos.

  2. Clean the data

    Raw data is almost never ready to use. Analysts spend most of their time to clean and organise files before doing anything else.

    Clean the data. Raw data is almost never ready to use. Analysts spend most of their time to clean and organise files before doing anything else.

  3. What does Lee discover about the raw rental logs?

    • The files are messy and need fixing first.
    • The files are already perfect for charts.
    • The files only need colourful fonts.

    Answer: The files are messy and need fixing first.

    Raw business data has errors, empty cells, and duplicate rows.

  4. One log says a rental lasted -20 minutes. Why must Lee fix this?

    • Wrong numbers make every total incorrect.
    • Negative numbers make screen colours break.
    • Analysts must only keep rows ending in zero.

    Answer: Wrong numbers make every total incorrect.

    Bad data leads to wrong totals and bad decisions.

  5. Complete the rule about an analyst's daily work.

    An analyst spends most time to ___ and organise messy files, not just make ___.

    Answer: An analyst spends most time to clean and organise messy files, not just make charts.

    Data cleaning takes up the largest share of an analyst's day.

  6. Build the daily task Lee performs on the rental logs.

    Answer: Lee removes duplicate rows to stop double counts

    Analysts fix flawed rows so managers can rely on the findings.

  7. Put Lee's steps in the right order:

    Answer: Receive raw rental logs → Remove duplicate rows and errors → Save the neat, cleaned table

    You must clean and verify data before you can use it.

  8. A coworker asks: 'Why not make the dashboard right now?' What is the best answer?

    • Messy data makes misleading charts.
    • Analysts are forbidden from opening charts on Mondays.
    • Raw files are always too small to draw.

    Answer: Messy data makes misleading charts.

    Cleaning happens first because all later steps depend on accurate data.

What to remember

  • Raw data is messy and full of mistakes.
  • Analysts spend much of their day cleaning data.
  • Clean data prevents false results.

Next in this course: Find useful patterns. It carries on in the Breni app.

The full The Data Analysis Process: From Question to Decision path