[R] Is there a function for this?

[Feng Qiu]

Hi everybody, I'm trying to do a statistic on the error rate of a prediction 
algorithm.

suppose this is the real category
[good, good, bad, bad, good, good, bad, bad]
this is the predicted category
[good, bad, bad, bad, good, good, good, bad]

I'm trying to do a statistic on the error rate for each group("good","bad"): 
what percentage of instances are predicted incorrectly for each group ?
Of course I can write a loop to do that, but is there a easy way to do that?

Thank you!

Best,

Feng