I am learning about nationality adjectives in Spanish. I came across the Puerto Ricans and I noticed the corresponding word in Spanish is "Puertorriqueño/a". I was not expecting to see a double "r". I then look at how "Puerto Rico" is written in Spanish: "Puerto Rico".
So why is there an extra "r" for Puerto Ricans? Does it have a linguistical reason? Are there other examples of this nature, whether for nationalities or other adjectives where the adjective gets a double letter when its base form does not have a double letter?