R/plot.rasch.mml.R

In alexanderrobitzsch/sirt: Supplementary Item Response Theory Models

## File Name: plot.rasch.mml.R
## File Version: 0.15



##############################################################
# S3 plot method for objects of class rasch.mml2
plot.rasch.mml <- function( x, items=NULL, xlim=NULL, main=NULL,
        ...){
    object <- x
    theta <- object$theta.k
    if ( is.matrix(theta) ){
       stop("Plot function is only applicable for unidimensional models")
                        }
    probs <- t(object$pjk)
    if ( is.null(items) ){ items <- 1:(nrow(probs) ) }
    I <- length(items)
    if (is.null(xlim)){ xlim <- c( min(theta), max(theta) ) }
    xlabplot <- expression( paste( theta ))
    ylabplot <- expression(paste(P,"(",X[i]==1, "|", theta, ")" ))
    if (object$irtmodel=="ramsay.qm"){
            xlabplot <- expression( paste( "log ",theta ))
                        }
    graphics::plot( theta, as.vector(probs[1,]), type="l", lty=1, xlab=xlabplot,
        ylab=ylabplot, xlim=xlim, ylim=c(0,1), main=main, ... )
    for (ii in 2:I){
        graphics::lines( theta, as.vector(probs[ii,]), type="l", lty=ii)
                    }
            }
##############################################################