Module 02 Activity

Scenario

Read a colleague's script and find the assumptions it makes silently.

What you build

An annotated review of a short script, plus a corrected version.

Steps

1. Rename every vague object so the name says what a row or a value is. Flag anything named after a base R function.
2. Find each place two vectors are combined and confirm they are the same length or that one has length one.
3. Find every comparison and decide what should happen when the value is NA. Replace any == NA with is.na().
4. Find every comparison of computed decimals and replace == with all.equal().
5. For each function the script calls, check the defaults that matter — especially na.rm — and state which the script is relying on.
6. Turn the calculation that appears three times into one function with a guard on its inputs.

Evidence to hand in

• The renamed objects, with the reason for each.
• The length audit of every vector combination.
• The NA handling decisions.
• The decimal comparisons you replaced.
• The defaults the script relies on.
• The extracted function with its guard.

Review checklist

• No object is named after a base R function.
• Every vector combination is length-checked, and no recycling warning is ignored.
• Missingness is tested with is.na() and never with ==.
• No computed decimal is compared with ==.
• The extracted function stops on impossible input rather than returning Inf or NaN.

Mark complete