Example of using a definition variable in a RAM model

x-->y;
def--> y; 
x*def-->y

# make up some data
require(umx); library(MASS)
N      = 500 # sample size, per group
Sigma  = matrix(c(1,.5,.5,1),2,2)
group1 = mvrnorm(N, c(1,2), Sigma) # Use mvrnorm from MASS package
group2 = mvrnorm(N, c(0,0), Sigma)
 
# Put the two groups together, create a definition variable,
# and make a list of which variables are to be analyzed (selVars)
xy              = rbind(group1,group2)      # Bind groups together by rows
dimnames(xy)[2] = list(c("x","y"))          # Add names
def             = rep(c(1,0),each=N);       # Add def var [2n] for group status
selVars         = c("x","y")                # Make selection variables object
df = data.frame(xy,def)
 
#############################################
# Make a model with moderation using a definition variable #
#############################################
m1 = mxModel("def_test", type="RAM", manifestVars= c("x", "y"), latentVars= "dummy", mxData(df, type= "raw"),
    mxPath(c("x", "y"), arrows= 2, free= TRUE),
    mxPath("one", to = c("x","y"), arrows= 1, free= TRUE),
    mxPath("dummy", value= 0, arrows= 2, free= FALSE),
    mxPath("one", to = "dummy", value= 0, free= FALSE),
    mxPath("x", to = "y"),
    mxPath("x", to = "dummy", values=0, free=FALSE, label = "data.def"),
    mxPath("dummy", to = "y")
)
m1 = mxRun(m1)