Occasionally the class of variable defined in the /wiki/spaces/DSDEV/pages/12943489 may not be the format required for the DataSHIELD function.
For example, the variable named cens - a censoring indicator for a survival model (1=died, 0=censored) - has been read into R. If you declare these as the names of the two levels of the variable in the categories tab of the /wiki/spaces/DSDEV/pages/12943489, it will then automatically be read in as a factor.
But if you want to use this variable as the outcome in a generalized linear model to analyse survival (e.g. a piecewise exponential regression model) it cannot be used as a factor - it has to be a numeric. It is possible to coerce variables into the class required for analysis. This is illustrated in the following example that coerces factor variables into numeric variables.
#What is the class of the variable cens after it has first been imported into the dataframe called EM?
> ds.class("EM$cens")
$study1
[1] "factor"
$study2
[1] "factor"
#Create a new variable called EVENT that is of class numeric
> ds.asNumeric("EM$cens","EVENT")
#Check that EVENT is of class numeric in both studies
> ds.class("EVENT")
$study1
[1] "numeric"
$study2
[1] "numeric"
