r - Quantmod: what's the difference between ROC(Cl(SPY)) and ClCl(SPY)

I feel like I'm missing something fundamental here, but I can't shake the feeling that these two series should be equivalent.

/edit: there is also dailyReturn(Cl(SPY)). I've seen all 3 of these methods used to calculate stock returns on various blogs, and I'm wondering which is 'correct.' They all give slightly different results...

/edit2: and there is also Delt(Cl(SPY)), which seems to be equivalent to ClCl(SPY)

Answer

TTR::ROC calculates log returns by default. quantmod::ClCl uses quantmod::Delt, which calculates arithmetic returns by default.

ROC(Cl(SPY), type="discrete") should match ClCl(SPY). Which is 'correct' depends on your purpose.