Question

I have a vector v. I would like to find the index of the minimum difference of the elements of a vector v which is less that 1e-2. How can I get the index?

    v = c(0.0002873771, 0.0006478544, 0.0092186701, 0.0267084167, 
        0.0457307072 , 0.3176459806)
    D = abs(diff(v)) < 1e-2

I want to get that the index = 1 not 1 and 2, just the minimum one.
If we have this vector

    v = c( 0.01144003, 0.04644231, 0.05527114, 0.31680614)
    D = abs(diff(v)) < 1e-2
    index = which.min(abs(diff(v)) < 1e-2 )

It give me the index = = 1 but actually my desire index is 2 not 1.

Answer 1

If you know that the minimum absolute difference is less than your tolerance, which.min is the correct function, and there is no need for D.

> which.min(abs(diff(v)))
[1] 1

This code, in your edited question:

index = which.min(abs(diff(v)) < 1e-2 )

is taking the which.min of a logical vector. Not what you intend. This is what you (probably) want:

v = c( 0.01144003, 0.04644231, 0.05527114, 0.31680614)
> which.min(abs(diff(v)))
[1] 2

To actually check for your tolerance, you can use any and if. Here, I assume you want NA to be returned if all differences exceed your tolerance:

min.difference.index <- if (any(abs(diff(v)) < 1e-2)) which.min(abs(diff(v))) else NA