extendrange
Numbers a bit outside the range of a vector

### Description

Expands range(x) symmetrically around mean(x).

### Usage

    extendrange(x, r = range(x, na.rm = TRUE), f = 0.05)

### Arguments

x | a vector of numbers or dates (or other classes for which range(x) and x+diff(x) work).
r | a vector of length two giving the range of x. If this is supplied, then x itself is ignored. Otherwise, it is the range of x, ignoring missing values.
f | a number: typically small. The range is expanded (or reduced, if f<0), by a factor of 1+f.

### Details

If x has only one unique value, then extendrange(x) is that value, twice.
Value
returns a two-long vector given by r + c(-1,1) * diff(r) * 0.05.
Examples

    extendrange(c(1,2,3,20))
    extendrange(as.Date(c("2015-09-01", "2016-01-15", "2015-12-30")), f=0.02)

Package grDevices version 6.1.5-18
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