月度总结
本课属于 Coddy R 学习旅程的“逻辑与流程”单元。第 61 课，共 64 课。
挑战
中等添加 MONTH 命令。确保之前步骤中的每个命令仍按原样正常工作。
MONTH <YYYY-MM>：只考虑日期以该月份开头的支出。回复2024-05: count 3, total 520.50, biggest rent，其中包含支出数量、保留两位小数的总额，以及当月金额最大的支出类别（如果有多个类别并列，选择第一个）。如果没有支出，则回复2024-05: no expenses。
提供的代码会将每一行输入作为一条命令传给 tracker()，并将每条返回的回复单独打印在一行上。日期的格式为 YYYY-MM-DD，类别是小写单词，输入中只包含目前介绍过的命令。
亲手试试
tracker <- function(commands) {
expenses <- data.frame(date = character(0), category = character(0), amount = numeric(0))
replies <- c()
for (cmd in commands) {
parts <- strsplit(cmd, " ")[[1]]
if (parts[1] == "ADD") {
amount <- suppressWarnings(as.numeric(parts[4]))
if (length(parts) != 4 || is.na(amount) || amount <= 0) {
replies <- c(replies, paste("invalid:", cmd))
} else {
expenses <- rbind(expenses, data.frame(date = parts[2], category = parts[3], amount = amount))
replies <- c(replies, sprintf("added %s %.2f", parts[3], amount))
}
} else if (parts[1] == "TOTAL") {
replies <- c(replies, sprintf("total: %.2f, count: %d", sum(expenses$amount), nrow(expenses)))
} else if (parts[1] == "CATEGORY") {
if (nrow(expenses) == 0) {
replies <- c(replies, "no expenses")
} else {
totals <- tapply(expenses$amount, expenses$category, sum)
replies <- c(replies, sprintf("%s: %.2f", names(totals), totals))
}
} else if (parts[1] == "TOP") {
n <- as.numeric(parts[2])
ranked <- expenses[order(-expenses$amount, expenses$date), ]
top <- head(ranked, n)
if (nrow(top) == 0) {
replies <- c(replies, "no expenses")
} else {
replies <- c(replies, sprintf("%s %s %.2f", top$date, top$category, top$amount))
}
}
}
replies
}
# 提供的输入/输出代码：保持原样
input <- suppressWarnings(readLines(file("stdin")))
cat(tracker(input), sep = "\n")
逻辑与流程中的所有课
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