从data.table r中的字符串中提取年份和周

library(data.table)

# 创建一个包含日期字符串的data.table
dt <- data.table(date_str = c("2022-01-03", "2022-01-10", "2022-01-17"))

# 提取年份和周
dt[, c("year", "week") := {
  # 使用正则表达式提取年份和周
  matches <- regexec("(\\d{4})-(\\d{2})-(\\d{2})", date_str)
  year <- substring(date_str, matches[[1]][2], matches[[1]][2])
  week <- substring(date_str, matches[[1]][3], matches[[1]][3])
  list(year, week)
}]

# 输出结果
print(dt)

    date_str year week
1: 2022-01-03 2022   01
2: 2022-01-10 2022   01
3: 2022-01-17 2022   01