Dear List,
 
I have the following code:
 
x <-c(0, 13.8333333333333, 38.1666666666667, 62.1666666666667, 85.9166666666667, 108.916666666667)
y <-c(1.77, 2.39, 3, 2.65, 2.62, 1.8)
Interpolated <- approx(x, y,xout=0:tail(x, n=1),method="linear")
plot(Interpolated)
 
in this code x is time in hours (cumulative), and y is a biological variable. I am using linear interpolation assuming getting from y(i) to y(i+1) is a linear path. I would like to calculate the time in this case that it takes to surpass the y value of 2 for the first time. If you look at the plot, you will see that the y value of 2 is crossed on 2 occasions: between the first and second value of y (ie:1.77 to 2.39) and the fifth and sixth value of y (ie2.62 and 1.8). In my case I really only care about the first "section" (ie: how long it takes to get from 1.77 to 2.0). Any thoughts on how I could calculate that chunk of the time would be greatly appreciated.
 
let me present it in a simpler idea wher I can actually tell you what the answer should be without having the code:
 
x <-c(0, 12, 24, 36, 48, 60)
y <-c(1.5, 2, 3, 2.65, 2.62, 1.8)
Interpolated <- approx(x, y,xout=0:tail(x, n=1),method="linear")
plot(Interpolated)
 
the answer in this case is 12 hours, which is the time spent in getting from 1.5 to 2...
 
hope I explained clearly what I am trying to do
 
appreciate the help,
 
Andras
 
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