languageR (version 1.0)

lags.fnc: Calculate vector at specified lag

Description

This function calculates for a given dependent variable the value of that variable at lag timesteps earlier in the time series of an experiment.

Usage

lags.fnc(dat, time="Trial", group = "Subject", depvar = "RT", lag=1)

Arguments

dat

A data frame with (minimally) a grouping factor, an time index for successive trails/events, and a behavioral measure

group

A grouping factor such as Subject

time

A sequential time index measure such as Trial number in an experimental list

depvar

The dependent variable, usually a chronometric measure such as RT

lag

The lag for which previous values are to be extracted

Value

• A vector with the values of the dependent variable at the specified lag. The by-group mean is substituted for the first lag timestep(s), for which there is/are no preceding value(s) for the dependent variable.

Examples

dfr = data.frame(Subject=c(rep("a", 5), rep("b", 5)),
                   Trial = c(rep(1:5,2)),
                   RT = rnorm(10, 500, 40))
  dfr$prevRT = lag.fnc(dfr, time="Trial", group="Subject", depvar="RT")
  dfr