Coercion and recycling contracts

The idea

An atomic R vector uses one underlying type. Combining numbers and text therefore creates a character vector rather than preserving a separate type for each element. This differs from a list. Inspect types at the boundary of a calculation, and parse text deliberately; silently accepting mixed input can move a failure far from its original cause.

Arithmetic recycles a shorter vector along a longer one. Exact recycling can be useful for a known repeated pattern, but it can also hide a length error without warning. A warning occurs for fractional recycling, not for every mismatch. If the contract requires one weight per observation, compare lengths explicitly before multiplication instead of treating the absence of a warning as validation.

x <- c(2,4,6,8)
cat(x + c(10,20), sep=",")
cat("\n", typeof(c(1,"2")), "\n", sep="")

12,24,16,28
character

The two offsets repeat exactly. Adding text to an atomic vector coerces the numeric entry to text.