From a vector, I want to select all elements within two standard deviations of the vector elements. Is there any R function for such selection?

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You need first to find the indices of all those elements within 2 standard deviations of the vector. Then you can use those indices to select such elements.

Here is an example:

> aa <- c(10,12,324,13,345,32,56,73,87,19,23,45,67, 20,42,120, 112)

>pos = abs(aa - mean(aa)) <= 2*sd(aa)

> pos

[1] TRUE TRUE FALSE TRUE FALSE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE

>bb <- aa[pos]

> bb

[1] 10 12 13 32 56 73 87 19 23 45 67 20 42 120 112

>

If you want to use one line code, you can combine two statements like this:

> bb <- aa[abs(aa - mean(aa)) <= 2*sd(aa)]

> bb

[1] 10 12 13 32 56 73 87 19 23 45 67 20 42 120 112