Detrends y by subtracting a linear trend in x, to create
a vector that is zero for its first and last finite value.
If the second parameter (y) is missing, then x is
taken to be y, and a new x is constructed with
seq_along(). Any NA values are left as-is.
Arguments
- x
a vector of numerical values. If y is not given, then
x is taken for y.
- y
an optional vector
Value
A list containing Y, the detrended version of y, and
the intercept a and slope b of the linear function of x
that is subtracted from y to yield Y.
Details
A common application is to bring the end points of a time series
down to zero, prior to applying a digital filter. (See examples.)
Examples
x <- seq(0, 0.9 * pi, length.out = 50)
y <- sin(x)
y[1] <- NA
y[10] <- NA
plot(x, y, ylim = c(0, 1))
d <- detrend(x, y)
points(x, d$Y, pch = 20)
abline(d$a, d$b, col = "blue")
abline(h = 0)
points(x, d$Y + d$a + d$b * x, col = "blue", pch = "+")
