如何用IfElse或Case_When在R中提取数据生成两列？

使用case_when实现 #

你可以在mutate中通过case_when根据字符串长度分别提取对应位置的数字，同时提取开头的1-2位数字：

library(dplyr)

# 示例数据
pc <- structure(list(Pitcnt = c("12 (3-2)", "7 (0-1)", "3 (0-2)", 
"8 (3-2)", "5 (2-2)", "7 (3-2)", "1 (0-0)", "2 (0-1)", "5 (1-2)", 
"10 (3-2)"), class = c("tbl_df", "tbl", "data.frame"), row.names = c(NA, 
-10L))

# 处理数据
pc_processed <- pc %>%
  mutate(
    # 提取开头的1或2位数字
    start_num = as.numeric(ifelse(nchar(Pitcnt) == 8, substr(Pitcnt, 1, 2), substr(Pitcnt, 1, 1))),
    # 根据字符串长度提取短横线前的数字到x列
    x = case_when(
      nchar(Pitcnt) == 8 ~ as.numeric(substr(Pitcnt, 5, 5)),
      nchar(Pitcnt) == 7 ~ as.numeric(substr(Pitcnt, 4, 4))
    ),
    # 根据字符串长度提取短横线后的数字到y列
    y = case_when(
      nchar(Pitcnt) == 8 ~ as.numeric(substr(Pitcnt, 7, 7)),
      nchar(Pitcnt) == 7 ~ as.numeric(substr(Pitcnt, 6, 6))
    )
  )

print(pc_processed)

基于正则表达式的更优方案 #

依赖字符串长度的方式不够灵活，使用正则表达式捕获组可以直接定位需要的数字，无需判断长度：

library(dplyr)
library(tidyr)

pc_processed <- pc %>%
  # 正则表达式捕获三个目标数字：开头1-2位、短横线前后各1位
  extract(Pitcnt, into = c("start_num", "x", "y"),
          regex = "^(\\d{1,2}) \\((\\d)-(\\d)\\)",
          convert = TRUE) # 自动转换为数值类型

print(pc_processed)

输出结果 #

两种方法都会得到如下结果：

# A tibble: 10 × 3
   start_num     x     y
       <int> <int> <int>
 1        12     3     2
 2         7     0     1
 3         3     0     2
 4         8     3     2
 5         5     2     2
 6         7     3     2
 7         1     0     0
 8         2     0     1
 9         5     1     2
10        10     3     2

内容的提问来源于stack exchange，提问作者Metsfan