nback.R

stimuli <- letters[1:9]

n = 2
K <- 36

stimuli_list <- vector(mode = "list", length = K)
response_list <- vector(mode = "list", length = K)

for (i in seq(K)){
  if (i <= n){
    stimuli_list[[i]] <- sample(stimuli, 1)
  } else {
    if (runif(1) >= 0.5) {
      stimuli_list[[i]] <- stimuli_list[[i-n]]
      response_list[[i]] <- 'same'
    } else {
      
      while (TRUE){
        
        stimuli_list[[i]] <- sample(stimuli, 1)
        if (stimuli_list[[i]] != stimuli_list[[i-n]]) {
          break 
        }
      }
      
      # just a check
      stopifnot(stimuli_list[[i]] != stimuli_list[[i-n]])
      
      response_list[[i]] <- 'different'
      
    }
  }
}

data_df <- tibble(stimulus = as.character(stimuli_list),
                  response = as.character(response_list))