Group by date and automatically change this:
Date1 Time1 Reading1
Date1 Time2 Reading2
Date1 Time3 Reading3
Date2 Time1 Reading1
Date2 Time2 Reading2
Date3 Time1 Reading1
Date3 Time2 Reading2
Date3 Time3 Reading3
Date3 Time4 Reading4

to this:
Date1 Time1 Reading1 Time2 Reading2 Time3 Reading3
Date2 Time1 Reading1 Time2 Reading2
Date3 Time1 Reading1 Time2 Reading2 Time3 Reading3 Time4
Reading4