最高分学生

本课属于 Coddy R 学习旅程的“逻辑与流程”单元。第 26 课，共 64 课。

挑战

中等

添加 TOP 命令。确保之前步骤中的每条命令仍和之前一样正常工作。

TOP：回复 Top: ，后面依次跟上平均分最高的学生姓名和保留一位小数的平均分，例如 Top: ada (92.0)。跳过没有成绩的学生。平均分相同时，选择姓名按字母顺序排在最前面的学生。如果没有学生有成绩，则回复 Top: none。

提供的代码会将每一行输入作为一条命令传给 gradebook()，并将每条返回的回复单独打印在一行上。姓名是一个小写单词，输入中只包含目前为止描述的命令。

亲手试试

average_text <- function(scores) {
  if (length(scores) == 0) "no grades" else sprintf("%.1f", mean(scores))
}

gradebook <- function(commands) {
  grades <- list()
  replies <- c()
  for (cmd in commands) {
    parts <- strsplit(cmd, " ")[[1]]
    name <- parts[2]
    if (parts[1] == "ADD") {
      if (name %in% names(grades)) {
        replies <- c(replies, paste(name, "already exists"))
      } else {
        grades[[name]] <- numeric(0)
        replies <- c(replies, paste("added", name))
      }
    } else if (parts[1] == "GRADE") {
      if (!(name %in% names(grades))) {
        replies <- c(replies, paste("no student", name))
      } else {
        score <- as.numeric(parts[3])
        grades[[name]] <- c(grades[[name]], score)
        replies <- c(replies, paste("recorded", score, "for", name))
      }
    } else if (parts[1] == "AVG") {
      if (!(name %in% names(grades))) {
        replies <- c(replies, paste("no student", name))
      } else {
        replies <- c(replies, paste0(name, ": ", average_text(grades[[name]])))
      }
    } else if (parts[1] == "REPORT") {
      for (student in sort(names(grades))) {
        replies <- c(replies, paste0(student, ": ", average_text(grades[[student]])))
      }
      replies <- c(replies, paste("Class average:", average_text(unlist(grades))))
    }
  }
  replies
}

# 提供的输入/输出代码：保持原样
input <- suppressWarnings(readLines(file("stdin")))
cat(gradebook(input), sep = "\n")