# Data Simulation

    library(abn)
    #> abn version 3.1.9 (2025-06-26) is loaded.
    #> To cite the package 'abn' in publications call: citation('abn').
    #>
    #> Attaching package: 'abn'
    #> The following object is masked from 'package:base':
    #>
    #>     factorial

In this vignette, we will simulate data from an additive Bayesian network and compare it to the original data.

# Fit a model to the original data

First, we will fit a model to the original data that we will use to simulate new data from. We will use the `ex1.dag.data` data set and fit a model to it.

    # Load example data
    mydat <- ex1.dag.data

    # Set the distribution of each node
    mydists <- list(b1="binomial",
                    p1="poisson",
                    g1="gaussian",
                    b2="binomial",
                    p2="poisson",
                    b3="binomial",
                    g2="gaussian",
                    b4="binomial",
                    b5="binomial",
                    g3="gaussian")

    # Build the score cache
    mycache <- buildScoreCache(data.df = mydat,
                               data.dists = mydists,
                               method = "bayes",
                               max.parents = 4)
    #> Warning: package 'INLA' was built under R version 4.5.0
    #> Loading required package: Matrix
    #> This is INLA_25.06.07 built 2025-06-11 18:54:45 UTC.
    #>  - See www.r-inla.org/contact-us for how to get help.
    #>  - List available models/likelihoods/etc with inla.list.models()
    #>  - Use inla.doc(<NAME>) to access documentation

    # Structure learning
    mp.dag <- mostProbable(score.cache = mycache)
    #> Step1. completed max alpha_i(S) for all i and S
    #> Total sets g(S) to be evaluated over: 1024

    # Estimate the parameters
    myfit <- fitAbn(object = mp.dag)

    # Plot the DAG
    plot(myfit)

plot of chunk fit_model

# Simulate new data

Based on the `abnFit` object, we can simulate new data. By default `simulateAbn()` synthesizes 1000 new data points.

    mydat_sim <- simulateAbn(object = myfit)
    str(mydat_sim)
    #> 'data.frame':    1000 obs. of  10 variables:
    #>  $ b1: Factor w/ 2 levels "0","1": 2 2 2 2 2 2 2 2 2 2 ...
    #>  $ b2: Factor w/ 2 levels "0","1": 1 1 1 1 2 1 1 2 2 2 ...
    #>  $ b3: Factor w/ 2 levels "0","1": 2 1 2 1 1 1 2 1 2 2 ...
    #>  $ b4: Factor w/ 2 levels "0","1": 2 2 2 2 2 2 2 2 2 2 ...
    #>  $ b5: Factor w/ 2 levels "0","1": 2 2 2 2 2 2 1 2 2 2 ...
    #>  $ g1: num  0.796 -0.92 0.167 -2.602 -0.432 ...
    #>  $ g2: num  0.112 -0.708 -1.621 0.115 1.504 ...
    #>  $ g3: num  0.703 -0.891 0.206 -0.55 -1.458 ...
    #>  $ p1: num  0 1 1 0 0 0 1 0 1 0 ...
    #>  $ p2: num  17 7 6 16 9 12 7 9 5 9 ...

In the background, the `simulateAbn()` function translates the `abnFit` object into a BUGS model and calls the `rjags` package to simulate new data.

Especially for debugging purposes, it can be usefull to manually inspect the BUGS file that is generated by `simulateAbn()`. This can be done by not running the simulation with `run.simulation = FALSE` and print the BUGS file to console with `verbose = TRUE`.

    # Simulate new data and print the BUGS file to the console
    simulateAbn(object = myfit,
                run.simulation = FALSE,
                verbose = TRUE)

To store the BUGS file for reproducibility or manual inspection, we can set the `bugsfile` argument to a file name to save the BUGS file to disk.

# Compare the original and simulated data

We can compare the original and simulated data by plotting the distributions of the variables.

    # order the columns of mydat equal to mydat_sim
    mydat <- mydat[, colnames(mydat_sim)]

    library(ggplot2)
    library(gridExtra)

    # Create a list of variables
    variables <- names(mydat)

    # Initialize an empty list to store plots
    plots <- list()

    # For each variable
    for (i in seq_along(variables)) {
      # Check if the variable is numeric
      if (is.numeric(mydat[[variables[i]]])) {
        # Create a histogram for the variable in mydat
        p1 <- ggplot(mydat, aes(!!as.name(variables[i]))) +
          geom_histogram(binwidth = 0.5, fill = "skyblue", color = "black") +
          labs(title = paste("mydat", variables[i]), x = variables[i], y = "Count") +
          theme_minimal()

        # Create a histogram for the variable in mydat_sim
        p2 <- ggplot(mydat_sim, aes(!!as.name(variables[i]))) +
          geom_histogram(binwidth = 0.5, fill = "skyblue", color = "black") +
          labs(title = paste("mydat_sim", variables[i]), x = variables[i], y = "Count") +
          theme_minimal()
      } else {
        # Create a bar plot for the variable in mydat
        p1 <- ggplot(mydat, aes(!!as.name(variables[i]))) +
          geom_bar(fill = "skyblue", color = "black") +
          labs(title = paste("mydat", variables[i]), x = variables[i], y = "Count") +
          theme_minimal()

        # Create a bar plot for the variable in mydat_sim
        p2 <- ggplot(mydat_sim, aes(!!as.name(variables[i]))) +
          geom_bar(fill = "skyblue", color = "black") +
          labs(title = paste("mydat_sim", variables[i]), x = variables[i], y = "Count") +
          theme_minimal()
      }

      # Combine the plots into a grid
      plots[[i]] <- arrangeGrob(p1, p2, ncol = 2)
    }

    # Print all plots
    do.call(grid.arrange, c(plots, ncol = 1))

plot of chunk unnamed-chunk-3

The plots show that the distributions of the original and simulated data are similar.