[R] problem with indicators for switch

[Roy Davy]

Hi, 
 
I am having some problems setting up some indicators and would appreciate any help.
I have some data called 'lights' with 3 variables called x, a and b. 
x - is the date
a - equals 1 to indicate an 'on' button is activated
b - equals 1 to indicate an 'off' button is activated 
 
Essentially i wannt to create 2 new variables c and d 
c - will reflect the current state of the light (1 being on)
d - will be a count for how many days the light has been on 
 
here's some data with the date omitted to illustrate what i have and what is required. 
 
a b c d
0 0 0 0
0 0 0 0
1 0 1 1
1 0 1 2
0 0 1 3
0 0 1 4
1 0 1 5
0 0 1 6
0 0 1 7
0 1 0 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
1 0 1 1
0 0 1 2
0 0 1 3
0 0 1 4
0 1 0 0
0 0 0 0
 
 After some considerable time i have managed to create variable c with a loop but it's really slow with the volume of data i have. Could anyone please show me how to do this efficiently? 
 
I hope this is clear... 
 
Thanks 
 
 
Roy