Page 4 of 8~104 min topic

Data: tables and simple plots

Measure whether the study table and plot works

Page 4 turns “it ran” into executable checks for the study-hours table plus hours-vs-pass plot.

~13 min this pageEvaluation

1Learn the idea

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Make the metric executable

Translate the claim into assertions or a tiny eval harness. The metric to protect is: mean hours, max hours, and plot file exists with xlabel/ylabel set. Always record the denominator (how many cases) beside any rate. A percentage without a denominator is marketing, not measurement.

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Run the checks

from pathlib import Path
assert Path('hours_vs_pass.png').exists()
print({'plot_exists':True,'xlabel':'hours','ylabel':'passed'})

Expected evidence: plot_exists True. A passing assertion proves only the behavior it names; broader usefulness still needs the chapter’s full limits.

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Say what the metric does not prove

Be explicit: beating the baseline (hand-computed mean of the four-row fixture) on this fixture does not prove behavior under wrong column names, or a plot that saves without axis labels. Label observations separately from conclusions so the next page inherits honest evidence about the study table and plot.

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Lab notebook: denominator discipline

Compute mean hours, max hours, and plot file exists with xlabel/ylabel set with the denominator written beside the rate every time. For this chapter, the evaluation set is intentionally tiny; that is allowed only if you say so in the evidence. Compare against hand-computed mean of the four-row fixture before celebrating.

Add one negative case aimed at wrong column names, or a plot that saves without axis labels. A suite with only happy cases cannot protect the study table and plot when the characteristic failure appears in review.

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Worked judgment

If a check is expensive or flaky, shrink it until it is deterministic on four-row study.csv with hours and passed columns. Flaky green builds teach the team to ignore gates. Record what this page does not prove so security-ops and mastery-ship inherit honest limits.

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Why this stage matters for the study table and plot

At the evaluation stage for data-tables-and-plots, the job is narrower than finishing a product demo. You are creating one progressive evidence piece about four-row study.csv with hours and passed columns that later pages inherit without redefining success. Keep that fixture small enough to inspect by hand, keep outputs copy-pasteable as text, and refuse to narrate this baseline as if it were a production SLA: hand-computed mean of the four-row fixture.

For this page specifically, success looks like metrics with explicit denominators and a negative case while still centering the user decision to inspect typical hours, an extreme value, and the hours/pass relationship. If you cannot point to a file, command, or assertion that proves that for the study table and plot, stay on this page instead of advancing.

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Extra mastery block

For data-tables-and-plots, write a transfer example that differs in one constraint from the chapter scenario. Keep the quality bar fixed. Explain which check still applies.

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Extra mastery block

For data-tables-and-plots, write a transfer example that differs in one constraint from the chapter scenario. Keep the quality bar fixed. Explain which check still applies.

Read

Extra mastery block

For data-tables-and-plots, write a transfer example that differs in one constraint from the chapter scenario. Keep the quality bar fixed. Explain which check still applies.

Go deeper

Before you start

Why this matters

Write one independent check that would catch a fake pass for this lab. Prefer a check tied to mean hours, max hours, and plot file exists with xlabel/ylabel set over a check that only asserts “no exception.”

In the wild

See how this idea shows up as a product and a company — then come back to the lesson. Skills transfer across vendors.

Check your understanding

Page assessment

Answer from memory. Completion is saved from this evidence, not from opening the next page.

1. Is the metric computed with an explicit denominator?
2. Does a failing gold case actually fail the harness?
3. Did you separate observations from conclusions?
4. What remains unproved after these checks?

All responses are required.