R/sequential.items.R

In CDM: Cognitive Diagnosis Modeling

## File Name: sequential.items.R
## File Version: 1.11

# converts a dataset with polytomous item responses
# into a dataset with sequential dichotomous items
sequential.items <- function( data )
{
    N <- nrow(data)
    I <- ncol(data)
    maxK <- apply( data, 2, max, na.rm=TRUE )
    dat.exp  <- matrix( NA, nrow=N, ncol=sum(maxK) )
    vv <- 1
    for (ii in 1:I){
        dat.ii <- data[,ii]
        kk <- 1
        dat.exp[, vv ] <- 1 * ( dat.ii >=kk )
        vv <- vv + 1     # column index
        if (maxK[ii]>1){
            for (kk in 2:maxK[ii]){
                dat.exp[, vv ] <- 1 * ( dat.ii >=kk )
                dat.exp[ dat.ii < kk - 1, vv ] <- NA
                vv <- vv + 1
            }
        }
    }
    #****
    # variable names
    varnames <- sapply( 1:I, FUN=function(ii){
                    if ( maxK[ii]==1 ){  v1 <- colnames(data)[ii] } else
                        { v1 <- paste0( colnames(data)[ii], "_Cat", 1:maxK[ii] ) }
                    v1
            } )
    colnames(dat.exp) <- unlist( varnames )
    dat.exp <- as.data.frame( dat.exp)
    # item information table
    iteminfo <- data.frame("item"=rep( colnames(data), maxK ) )
    iteminfo$itemindex <- match( iteminfo$item, colnames(data) )
    iteminfo$category <- unlist( sapply( 1:I, FUN=function(ii){ 1:(maxK[ii])  },
                                simplify=FALSE)   )
    iteminfo$pseudoitem <- colnames(dat.exp)
    res <- list( "dat.expand"=dat.exp, "iteminfo"=iteminfo,
                        "maxK"=maxK)
    return(res)
}