组内的唯一ID [英] Unique ID within group

问题描述

我有以下数据集:

data <- data.table(match = c(1,1,1,1,2,2,2,2), 
player = c("Dave", "Dave", "Dennis", "Dave", "Jake", "Jake", "Josh", "Jake"),
 team = c("Australia", "Australia", "Australia", "Australia", "England", "England", "England", "England"))

我想创建一个ID变量，该变量指示给定比赛中团队中每个球员的位置.对于Give数据集，该变量将显示为:

I want to create an ID variable that indicates the position of each player in a team for a given match. The variable, for the give dataset, would look go:

ID = c(1,1,2,1,1,1,2,1)

我尝试使用group_by并在组内分配行号，但这不起作用.关于如何执行此操作的任何想法?

I have tried using group_by and assigning row number within a group but that isn't working. Any idea on how to do this?

推荐答案

我们可以使用 match (该函数)

We can use match (the function)

library(data.table)
data[, ID := match(player, unique(player)), match]

或使用 factor

data[, ID := as.integer(factor(player, levels = unique(player))), match]
data
#   match player      team ID
#1:     1   Dave Australia  1
#2:     1   Dave Australia  1
#3:     1 Dennis Australia  2
#4:     1   Dave Australia  1
#5:     2   Jake   England  1
#6:     2   Jake   England  1
#7:     2   Josh   England  2
#8:     2   Jake   England  1

---

dplyr 中的

类似选项将是

---

Similar option in dplyr would be

library(dplyr)
data %>%
   group_by(match) %>%
   mutate(ID = match(player, unique(player)))

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