combine rows with same values and apply a function to get a ratio

Asked Feb 06 '17 at 19:30

Active Feb 06 '17 at 19:48

Viewed 67 times

I have a dataset looks like this

time   value
0.1    2
0.1    3
0.2    2
0.2    4
0.2    1

I also have a threshold value threshold = 2.5

I want to combine the rows with the same time point and calculate the ratio above the threshold and return a table like this:

time    value
0.1     0.50
0.2     0.33

I have tried to use data.table to combine all the rows with same time points but I am having some trouble to come up a function to calculate ratio at each time point. I know that I could write some for loop but I am wondering if there's a more R way to solve this problem.

My thought is something like this:

results <- dt[,some_function(value, threshold),by=time]

Thank you in advance.

edited Feb 06 '17 at 19:48

asked Feb 06 '17 at 19:30

RLFT

2

`mean(value > threshold)` is your `some_function` – Gregor Thomas Feb 06 '17 at 19:34
Fyi, grouping by floats is dangerous, since `1. + .2 != .3` etc. http://stackoverflow.com/q/9508518/ – Frank Feb 06 '17 at 19:40
Also, shouldn't the second row be `0.2,0.33` – Silence Dogood Feb 06 '17 at 19:41
@Osssan thanks:) just edited. – RLFT Feb 06 '17 at 19:49
@Gregor Thank you!! – RLFT Feb 06 '17 at 20:01
@Frank I see. I will keep that in mind. Thank you! – RLFT Feb 06 '17 at 20:02

combine rows with same values and apply a function to get a ratio

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