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Find the value of x corresponding to the maximum or minimum of y

You have two numeric vectors, x and y, of the same length and want to find the value of x where y attains its maximum value

Solution: Combine the which.max or which.min function with indexing.

> x <- seq(0, pi/2, .2)
> y <- sin(2*x)
> x[which.max(y)]
[1] 0.8

See rule 2.5 in The R Primer for more information.

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