Hi Arranroots,
The date of the diary is 1871, and as far as I can make out R. R. Roberts was the conductor/leader of the Talsarnau choir.
My grandfather (the diary writer) was studying at the Royal Academy in London (he became a noted Welsh Victorian composer of both sacred and secular music) and the choir had/was performed/performing one of his numbers.
As to the name pattern, I agree with you - my grandfather was called Robert Roberts Roberts on his birth certificate, his sister married a William Williams Williams, and another figure from his diary was called Evan Evans.
Nobody I have spoken to to can give an explanation!
Thanks for all your help.
Regards
Quarryman