create MCAR data (from package `mi`).

alt-gen-MCAR-fun

mi:::.create.missing
function (data, pct.mis = 10) 
{
    n <- nrow(data)
    J <- ncol(data)
    if (length(pct.mis) == 1) {
        n.mis <- rep((n * (pct.mis/100)), J)
    }
    else {
        if (length(pct.mis) < J) 
            stop("The length of missing does not equal to the column of the data")
        n.mis <- n * (pct.mis/100)
    }
    for (i in 1:ncol(data)) {
        if (n.mis[i] == 0) {
            data[, i] <- data[, i]
        }
        else {
            data[sample(1:n, n.mis[i], replace = FALSE), i] <- NA
        }
    }
    return(as.data.frame(data))
}
<environment: namespace:mi>