R语言：将特定格式字符日期列转为日期类型且避免生成NA值

现有如下结构的R数据框，其中Start_Date和End_Date为字符型日期列，尝试转换为日期类型时部分值出现NA，期望最终输出格式为mm/dd/yyyy：

structure(list(Start_Date = c("Dec 12, 2017", "Oct 19, 2022","Oct 3, 2022"), 
               End_Date = c("Dec 25, 2017", "Dec 19, 2022",  "Dec 1, 2022"), 
               Completion = c("100% completed", "34% completed",  "62% completed")), 
          row.names = c(NA, -3L), class = c("tbl_df",  "tbl", "data.frame"))

出现NA的核心原因是日期格式指定错误——未兼容日部分为单数字的情况（如Oct 3, 2022），以下两种方法可完美解决：

方法1：使用lubridate包（推荐） #

lubridate能自动识别多种日期格式，无需手动匹配格式字符串，对单/双数字日期均兼容：

# 安装并加载包
install.packages("lubridate")
library(lubridate)

# 加载数据
df <- structure(list(Start_Date = c("Dec 12, 2017", "Oct 19, 2022","Oct 3, 2022"), 
               End_Date = c("Dec 25, 2017", "Dec 19, 2022",  "Dec 1, 2022"), 
               Completion = c("100% completed", "34% completed",  "62% completed")), 
          row.names = c(NA, -3L), class = c("tbl_df",  "tbl", "data.frame"))

# 转换为日期类型
df$Start_Date <- mdy(df$Start_Date)
df$End_Date <- mdy(df$End_Date)

# 若需转为`mm/dd/yyyy`字符格式，执行以下步骤
df$Start_Date <- format(df$Start_Date, "%m/%d/%Y")
df$End_Date <- format(df$End_Date, "%m/%d/%Y")

方法2：使用base R的as.Date函数 #

需指定正确的格式字符串：%b匹配月份缩写，%d兼容单/双数字日，%Y匹配4位年份：

# 加载数据
df <- structure(list(Start_Date = c("Dec 12, 2017", "Oct 19, 2022","Oct 3, 2022"), 
               End_Date = c("Dec 25, 2017", "Dec 19, 2022",  "Dec 1, 2022"), 
               Completion = c("100% completed", "34% completed",  "62% completed")), 
          row.names = c(NA, -3L), class = c("tbl_df",  "tbl", "data.frame"))

# 转换为日期类型
df$Start_Date <- as.Date(df$Start_Date, format = "%b %d, %Y")
df$End_Date <- as.Date(df$End_Date, format = "%b %d, %Y")

# 格式化为`mm/dd/yyyy`字符格式
df$Start_Date <- format(df$Start_Date, "%m/%d/%Y")
df$End_Date <- format(df$End_Date, "%m/%d/%Y")

最终数据框如下：

# A tibble: 3 × 3
  Start_Date End_Date   Completion    
  <chr>      <chr>      <chr>         
1 12/12/2017 12/25/2017 100% completed
2 10/19/2022 12/19/2022 34% completed 
3 10/03/2022 12/01/2022 62% completed 

注：若需保留日期类型而非字符类型，跳过format()步骤即可。

内容的提问来源于stack exchange，提问作者Soph2010