A mixture of array and functional paradigms; writing efficient code in R requires basically the same type of thinking like in APL or J/Q/K and friends. Historically, R is a sort of a Scheme-based implementation of S, an earlier language which was basically a mixture of APL and Fortran that a statistician would use (i.e. not get discouraged by a bizarre syntax or for-pyramids). Syntax is probably an effect of the fact that both C and S were co-evolving in the same institution.

Both APL and R promote interactive exploratory programming. Both are strong in computational programming and intended primarily for domain experts, though over the years APL has drifted more into a domain for developers.

In my opinion, APL's array capabilities are far stronger and notation less noisy, i.e. less syntax and punctuation. R seems to have been developed with tools like Lex and Yacc and the language has a certain look and feel.