lagVar {epicalc} | R Documentation |
Create a vector of lagged or subsequent value in a long form longitudinal data
lagVar(var, id, time, lag.unit=1)
var |
variable to create the lag |
id |
subject identification field |
time |
time of measurement |
lag.unit |
lag number of visits |
Data must be in long format having variable to create the lag, id and time.
The default value of lag.unit is 1. When the number is negative, the next measured is created instead.
Virasakdi Chongsuvivatwong <cvirasak@medicine.psu.ac.th>
'lag'
## Identification of the tree that became smaller during followup data(Sitka, package="MASS") use(Sitka) lag1.size <- lagVar(var=size, id=tree, time=Time, lag=1) data.frame(tree=tree, time=Time, size=size, lag1.size=lag1.size) [1:20,] # Answer data.frame(Time, tree, size, lag1.size) [which(lag1.size > size),] # Alternatively next.size <- lagVar(size, tree, Time, lag=-1) data.frame(tree=tree, time=Time, size=size, next.size=next.size) [1:20,] data.frame(Time, tree, size, next.size) [which(size > next.size),]