Module 02 Summary

What this module established

R works on whole vectors, which removes most loops and introduces one hazard: recycling repeats a shorter vector silently when the lengths divide evenly, so a length mismatch can produce a plausible wrong answer with no warning at all.

Carry forward

• Use <- for assignment and mind the space — x < -5 is a comparison and R will not tell you which you meant.
• NA is unknown, so any comparison with it returns NA. Test with is.na(), and decide deliberately what happens to those rows.
• Computed decimals are never exactly equal. Use all.equal().
• Read a function's argument defaults before its description. na.rm = FALSE is why a mean of a column with one gap returns NA.

Before moving on

Move on when you can explain why sum(scores > 80) returned NA and give two different correct fixes.

Mark complete