lengths

Flag sapply(x, length), which is the purpose-built lengths(x)—faster (a single C pass instead of an R call per element) and clearer. Both return an integer vector and keep x’s names by default.

The rule fires only on the clean two-positional-argument shape and only when sapply resolves to base R and length is not locally rebound; a redefinition of either is left alone.

Per-element lengths of a list:

n <- sapply(x, length)

warning: lengths
 --> example.R:1:6
  |
1 | n <- sapply(x, length)
  |      ^^^^^^^^^^^^^^^^^ `sapply(x, length)` is the faster, clearer `lengths(x)`
  = help: Use `lengths(x)`.

After applying the fix:

n <- lengths(x)