按四分位数、均值或中位数分组，返回名称

getID.R

getID = function(exp_value, method){
  # compute threshold according to method parameter
  if(method=="quartile"){
    symbol_stat <- summary(exp_value)
    ths1 <- as.numeric(symbol_stat[2])
    ths2 <- as.numeric(symbol_stat[5])
    down_id <- names(exp_value[exp_value<=ths1])
    up_id <- names(exp_value[exp_value>=ths2])
  }else if(method=="mean"){
    ths <- mean(exp_value)
    down_id <- names(exp_value[exp_value<=ths])
    up_id <- names(exp_value[exp_value>ths])
  }else if(method=="median"){
    ths <- median(exp_value)
    down_id <- names(exp_value[exp_value<=ths])
    up_id <- names(exp_value[exp_value>ths])
  }
  return(list(down_id, up_id))
}