如何基于日期条件在R语言DataFrame中创建标记新列？

问题原因 #

代码执行失败的核心是两个DataFrame的day列类型不匹配：

• df1的day是Date类（仅日期）
• df2的day是POSIXct类（带时间戳的日期时间类型）
  同时df2中存在NA值，会干扰匹配逻辑。

解决方案 #

先统一日期类型并清理无效值，再执行匹配：

步骤1：转换df2的日期类型并过滤NA #

# 将df2的day转换为Date类型，同时剔除NA值
prom_days <- as.Date(na.omit(df2$day))

步骤2：为df1添加prom列 #

因为df1是data.table，提供两种实现方式：

方式1：基础R语法

df1$prom <- ifelse(df1$day %in% prom_days, "*", "")

方式2：data.table原生语法（大数据量下更高效）

df1[, prom := ifelse(day %in% prom_days, "*", "")]

验证结果 #

执行后，df1中day为2018-01-20的行，prom列会被标记为*，其余行则为空字符串，完全符合预期输出。

完整可复现代码 #

# 加载数据
df1 <- structure(list(time = structure(c(1514764916, 1514764916, 1514765231, 
                                         1514765364, 1514765364, 1514767166, 1514767919, 1514767919, 1514767919, 
                                         1514767919, 1514767919, 1514767919, 1514768104, 1514768214, 1514768214, 
                                         1514768214, 1514768214, 1514768214, 1514768214, 1514770106, 1516406400
), tzone = "UTC", class = c("POSIXct", "POSIXt")), transactID = c(2278968, 
                                                                  2278968, 2255797, 2278968, 2278968, 2257125, 2278968, 2278968, 
                                                                  2278968, 2278968, 2278968, 2278968, 2255111, 2278968, 2278968, 
                                                                  2278968, 2278968, 2278968, 2278968, 2255111, 2255111), itemID = c(450, 
                                                                                                                                    83, 7851, 450, 83, 9375, 450, 83, 19, 297, 295, 109, 2049, 19, 
                                                                                                                                    83, 295, 297, 450, 109, 4322, 4322), order = c(1, 1, 2, 1, 1, 
                                                                                                                                                                                   1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1), salesPrice = c(17.42, 
                                                                                                                                                                                                                                                   5.19, 20.47, 17.42, 5.19, 31.02, 17.42, 5.19, 77.64, 43.53, 37.79, 
                                                                                                                                                                                                                                                   5.8, 35.75, 77.64, 5.19, 37.79, 43.53, 17.42, 5.8, 22.86, 22.86
                                                                                                                                                                                   ), day = structure(c(17532, 17532, 17532, 17532, 17532, 17532, 
                                                                                                                                                                                                        17532, 17532, 17532, 17532, 17532, 17532, 17532, 17532, 17532, 
                                                                                                                                                                                                        17532, 17532, 17532, 17532, 17532, 17551), class = "Date")), row.names = c(NA, 
                                                                                                                                                                                                                                                                                   -21L), class = c("data.table", "data.frame"))

df2 <- structure(list(day = structure(c(NA, 1531440000, 1530403200, 
1530489600, 1530748800, 1531267200, 1530662400, 1531008000, 1531094400, 
1530316800, 1530835200, 1531180800, 1530576000, 1531353600, 1530921600, 
1516402800), tzone = "", class = c("POSIXct", "POSIXt"))), row.names = c(NA, 
-16L), class = c("tbl_df", "tbl", "data.frame"))

# 处理日期并生成标记列
prom_days <- as.Date(na.omit(df2$day))
df1[, prom := ifelse(day %in% prom_days, "*", "")]

# 查看目标行结果
print(df1[day == "2018-01-20"])

内容的提问来源于stack exchange，提问作者JAdel