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Last data update: 2014.03.03

R: ~ Function: reduceNbTimes ~

reduceNbTimes

R Documentation

~ Function: reduceNbTimes ~

Description

reduceNbTimes simplify some trajectories (in long format) by reducing their number of points.

Usage

  reduceNbTimes(trajLong, nbPoints, spar=NA)

Arguments

trajLong

[data.frame]: data.frame that hold the trajectories in long format. The data.frame has to be (no choice!) in the following format: the first column should be the individual indentifiant. The second should be the times at which the measurement are made. The third one should be the measurement.

`nbPoints`	[`numeric`]: fixe the number of that the simplified trajectories should have.
`spar`	[`numeric`]: smoothing parameter that is used if the trajectories shall be smoothed before being simplified.

Details

reduceNbTimes simplify some trajectories by reducing their number of points. The trajectories should be in long format. If a value is given to spar (different from NA), trajectories are smoothed using smooth.spline.

The reduction of the number of point is done using a variation of Douglas-Peucker algorithme based on the number of points instead of an epsilon.

Value

A data.frame holding the simplified trajectories, in long format.

Author(s)

Christophe Genolini

Examples

  require(lattice)

  ### Some artificial data
  g <- function(x)dnorm(x,3)+dnorm(x,7)+x/10
  dn <- data.frame(id=rep(1:20,each=101),
    times=rep((0:100)/10,times=20),
    traj=rep(g((0:100)/10),20)+rep(runif(20),each=101)+rnorm(20*101,,0.1))

  xyplot(traj ~ times, data=dn, groups=id,type="l")

  ### Reduction to 50 points
  dn2 <- reduceNbTimes(trajLong=dn,nbPoints=50)
  xyplot(traj ~ times, data=dn2, groups=id,type="l")

  ### Reduction to 20 points
  dn3 <- reduceNbTimes(trajLong=dn,nbPoints=20)
  xyplot(traj ~ times, data=dn3, groups=id,type="l")

  ### Smoothing then reduction to 20 points
  dn4 <- reduceNbTimes(trajLong=dn,nbPoints=20,spar=0.5)
  xyplot(traj ~ times, data=dn4, groups=id,type="l")