match_fun.R

library(Matching)
data(lalonde)

run_iter_maching <- function(data, iters = 3) 
{
  
  # Setting up variables
  sample <- data
  ctrls <- list()
  treats <- list()
  
  for (i in 1:iters) {
    
    # Run matching
    m <- Match(sample$re78, sample$treat, 
          cbind(sample$age, sample$educ, sample$re74),
          M=1, ties=FALSE)
    
    # Save indexes
    ctrls[[i]] <- m$index.control
    treats[[i]] <- m$index.treated
    
    # Drop matched controls
    sample <- sample[-m$index.control, ]
  }
  
  # Get treated units that were matched every timei
  always_treat <- Reduce(intersect, treats)
  
  # Store matches
  match_out <- list()
  
  # For each remaining treated unit, find its control
  for (t_idx in always_treat)
  {
    # Create storage for the three controls
    this_ctrls <- c()
    
    # For each iteration
    for (i in 1:iters) 
    {
      # Find the correct index in the index.treated (Redundant when not LATE)
      inner_t_idx <- match(t_idx, treats[[i]])
      
      # Find corresponding control matched
      this_ctrls[i] <- ctrls[[i]][inner_t_idx]
    }
    
    # Save three controls
    match_out[[t_idx]] <- this_ctrls
  }
  
  return(match_out)
}

match_out <- run_iter_maching(lalonde)