comparison.pvalue <- function(index1, index2){
  if (index1 != index2){
    for (i in 1:length(index.rank.dunn.test$comparisons)){
      if ((index1 %in% index.rank.dunn.test$comparisons[i]) &
          (index2 %in% index.rank.dunn.test$comparisons[i])){
        j <- i
      }
    }
    # i <- which(str_detect(index.rank.dunn.test$comparisons, index1) &
    #              str_detect(index.rank.dunn.test$comparisons, index2))
    p.value <- index.rank.dunn.test$P.adjusted[j]
  } else{
    p.value <- 1
  }

  output <- p.value
  return(output)
}