how to introduce missing data for complete data

Here's a suggestion.

The sample() function takes random samples of sets. See
  ?sample
The set you want to take a random sample from is the rows of your data.
Represent the rows by their row numbers.
To get a vector of row numbers, you can use the seq() function. See
  ?seq

Let's suppose your data is in a data frame named 'mydat', and you want to
introduce 10 instances of missing data.

nr <- nrow(mydat)
set.to.missing <- sample( seq(nr) , 10)
mydat$Amount[set.to.missing] <- NA

A simplified example of the core idea is:

how to introduce missing data for complete data

Thread (3 messages)