R/bivariate_table_statistics.R

In CDM: Cognitive Diagnosis Modeling

## File Name: bivariate_table_statistics.R
## File Version: 0.06

bivariate_table_statistics <- function( freqtable, values=NULL)
{
    freqtable <- expand_matrix(x=freqtable)
    K <- nrow(freqtable)
    if (is.null(values)){
        values <- seq(0,K-1)
    }
    #--- first item
    freq1 <- rowSums(freqtable)
    res <- univar_table_statistics(freq=freq1)
    M1 <- res$M
    SD1 <- res$SD
    K1 <- sum( freq1 > 0 )
    #--- second item
    freq2 <- colSums(freqtable)
    res <- univar_table_statistics(freq=freq2)
    M2 <- res$M
    SD2 <- res$SD
    K2 <- sum( freq2 > 0 )
    #--- bivariate statistics
    valuesM <- outer( values, values )
    probs <- freqtable / sum( freqtable )
    cov1 <- sum( probs * valuesM ) - M1 * M2
    cor1 <- cov1 / SD1 / SD2
    #--- output
    res <- list( cov=cov1, cor=cor1, M1=M1, SD1=SD1, K1=K1, M2=M2, SD2=SD2, K2=K2)
    return(res)
}