interp1 {signal}

Interpolation

Description

Interpolation methods, including linear, spline, and cubic interpolation.

Usage

interp1(x, y, xi, method = c("linear", "nearest", "pchip", "cubic", "spline"), 
        extrap = NA, ...)

Arguments

x, y

vectors giving the coordinates of the points to be interpolated. x is assumed to be strictly monotonic.

xi

points at which to interpolate.

method

one of "linear", "nearest", "pchip", "cubic", "spline".

extrap

if TRUE or 'extrap', then extrapolate values beyond the endpoints. If extrap is a number, replace values beyond the endpoints with that number (defaults to NA).

...

for method='spline', additional arguments passed to splinefun.

Details

The following methods of interpolation are available:

'nearest': return nearest neighbour

'linear': linear interpolation from nearest neighbours

'pchip': piecewise cubic hermite interpolating polynomial

'cubic': cubic interpolation from four nearest neighbours

'spline': cubic spline interpolation–smooth first and second derivatives throughout the curve

Value

The interpolated signal, an array of length(xi).

Author(s)

Original Octave version by Paul Kienzle [e-mail]. Conversion to R by Tom Short.

References

Octave Forge https://octave.sourceforge.io/

See Also

approx, filter, resample, interp, spline

Examples

xf <- seq(0, 11, length=500)
yf <- sin(2*pi*xf/5)
#xp <- c(0:1,3:10)
#yp <- sin(2*pi*xp/5)
xp <- c(0:10)
yp <- sin(2*pi*xp/5)
extrap <- TRUE
lin  <- interp1(xp, yp, xf, 'linear', extrap = extrap)
spl  <- interp1(xp, yp, xf, 'spline', extrap = extrap)
pch  <- interp1(xp, yp, xf, 'pchip', extrap = extrap)
cub  <- interp1(xp, yp, xf, 'cubic', extrap = extrap)
near <- interp1(xp, yp, xf, 'nearest', extrap = extrap)
plot(xp, yp, xlim = c(0, 11))
lines(xf, lin, col = "red")
lines(xf, spl, col = "green")
lines(xf, pch, col = "orange")
lines(xf, cub, col = "blue")
lines(xf, near, col = "purple")