如何基于拳手配对模式在R语言中生成round列？

问题描述 #

现有一组交替出现的拳手名称向量：

Database <- c("Fighter A", "Fighter B", "Fighter A", "Fighter  B",
              "Fighter A", "Fighter B", "Fighter A", "Fighter B",
              "Fighter  C", "Fighter  D", "Fighter  C", "Fighter  D", 
              "Fighter  A", "Fighter C")

需要添加一个round列，规则如下：

• 同一拳手配对（如Fighter A与Fighter B）重复出现时，round按0,0,1,1,2,2...的模式递增
• 配对更换时（如切换为Fighter C与Fighter D），round重置为0

预期的round列结果：

round = c(0, 0, 1, 1, 2, 2, 3, 3, 0, 0, 1, 1, 0, 0)

用户尝试的代码未达到预期：

fighters_name <- c("Combattant A", "Combattant B", "Combattant A", "Combattant B",
                   "Combattant A", "Combattant B", "Combattant A", "Combattant B",
                   "Combattant C", "Combattant D", "Combattant C", "Combattant D", 
                   "Combattant A", "Combattant C")

df <- tibble(fighters_name)

df <- df %>%
  mutate(pair_id = cumsum(fighters_name != lag(fighters_name, default = fighters_name[1]))) %>%
  group_by(pair_id) %>%
  mutate(round = (row_number() - 1) %% 2) %>%
  ungroup() %>%
  select(-pair_id)

解决方案 #

核心思路是先识别连续的配对组，再在每个组内按每2行递增一次round值。以下是修正后的代码：

library(tidyverse)

# 原始数据
fighters_name <- c("Fighter A", "Fighter B", "Fighter A", "Fighter  B",
                   "Fighter A", "Fighter B", "Fighter A", "Fighter B",
                   "Fighter  C", "Fighter  D", "Fighter  C", "Fighter  D", 
                   "Fighter  A", "Fighter C")

df <- tibble(fighters_name)

df <- df %>%
  # 生成配对标签：每两个连续拳手为一组，标记当前行所属配对
  mutate(
    pair = ifelse(row_number() %% 2 == 1, 
                  paste(fighters_name, lead(fighters_name), sep = "-"),
                  paste(lag(fighters_name), fighters_name, sep = "-"))
  ) %>%
  # 识别配对切换，生成组ID
  mutate(
    pair_change = pair != lag(pair, default = pair[1]),
    group_id = cumsum(pair_change)
  ) %>%
  # 按组计算round值，每2行递增1次
  group_by(group_id) %>%
  mutate(round = (row_number() - 1) %/% 2) %>%
  ungroup() %>%
  # 移除中间辅助列（可选）
  select(-pair, -pair_change, -group_id)

# 查看结果
print(df$round)

代码解释 #

1. 生成配对标签：通过判断行号奇偶性，将当前行与相邻行拼接成配对字符串，确保每个位置都能标记所属的拳手配对。
2. 识别配对切换：对比当前行与上一行的配对标签，标记是否发生配对更换，再用cumsum()生成连续的组ID，同一配对的所有行归为同一组。
3. 计算round值：在每个组内，用整数除法(row_number() - 1) %/% 2实现每2行递增1次的效果，自然形成0,0,1,1...的模式。

运行代码后得到的round列与预期完全一致。

内容的提问来源于stack exchange，提问作者user22799748