Randomly insert NAs into dataframe proportionaly

Question

I have a complete dataframe. I want to 20% of the values in the dataframe to be replaced by NAs to simulate random missing data.

A <- c(1:10)
B <- c(1         


        

Answer 1

May i suggest a first function (ggNAadd) designed to do this, and improve it with a second function providing graphical distribution of the NAs created (ggNA)

What is neat is the possibility to input either a proportion of a fixed number of NAs.

ggNAadd = function(data, amount, plot=F){
  temp <- data
  amount2 <- ifelse(amount<1, round(prod(dim(data))*amount), amount)
  if (amount2 >= prod(dim(data))) stop("exceeded data size")
  for (i in 1:amount2) temp[sample.int(nrow(temp), 1), sample.int(ncol(temp), 1)] <- NA
  if (plot) print(ggNA(temp))
  return(temp)
}

And the plotting function:

ggNA = function(data, alpha=0.5){
  require(ggplot2)
  DF <- data
  if (!is.matrix(data)) DF <- as.matrix(DF)
  to.plot <- cbind.data.frame('y'=rep(1:nrow(DF), each=ncol(DF)), 
                              'x'=as.logical(t(is.na(DF)))*rep(1:ncol(DF), nrow(DF)))
  size <- 20 / log( prod(dim(DF)) )  # size of point depend on size of table
  g <- ggplot(data=to.plot) + aes(x,y) +
    geom_point(size=size, color="red", alpha=alpha) +
    scale_y_reverse() + xlim(1,ncol(DF)) +
    ggtitle("location of NAs in the data frame") +
    xlab("columns") + ylab("lines")
  pc <- round(sum(is.na(DF))/prod(dim(DF))*100, 2) # % NA
  print(paste("percentage of NA data: ", pc))
  return(g)
}

Which gives (using ggplot2 as graphical output):

ggNAadd(df, amount=0.20, plot=TRUE)
## [1] "percentage of NA data:  20"
##     A  B  c
## 1   1 11 21
## 2   2 12 22
## 3   3 13 23
## 4   4 NA 24
## ..

Of course, as mentioned earlier, if you ask too many NAs the actual percentage will drop because of repetitions.