获取data.table中关键字的索引

# 导入data.table库
library(data.table)

# 创建示例data.table
dt <- data.table(x = c(1, 2, 3, 4, 5), y = c("a", "b", "c", "d", "e"))

# 获取满足条件的行索引
index <- which(dt$x == 3)
print(index)

[1] 3

# 导入data.table库
library(data.table)

# 创建示例data.table
dt <- data.table(x = c(1, 2, 3, 4, 5), y = c("a", "b", "c", "d", "e"))

# 设置关键字
setkey(dt, x)

# 查询关键字的索引
index <- J(3)
result <- dt[index]
print(result)

   x y
1: 3 c

# 导入data.table库
library(data.table)

# 创建示例data.table
dt <- data.table(x = c(1, 2, 3, 4, 5), y = c("a", "b", "c", "d", "e"))

# 获取关键字在指定列中的索引
index <- which(get("keyword", envir = environment()) == dt$x)
print(index)