Dear R users,
It may be very simple but it is being difficult for me.
I'd like to calculate the difference in percent between to measures.
My data looks like this:
set.seed(123)
df1 <- data.frame(measure = rep(c("A1", "A2", "A3"), each=3),
water = sample(c(100:200), 9),
tide = sample(c(-10:+10), 9))
df1
# What I want to calculate is:
# tide_[A2] / water_[A1],
# tide_[A3] / water_[A2]
# This 'works' for the example, but I am
# looking for a more general solution.
df1$tide_diff <- ave(df1$tide, FUN=function(L) L /
c(NA, NA, NA, df1$water)) * 100
df1
Thanks for any help!
Patrick
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