第一次标记基于参数的记录出现在r数据框中

我们可以按“ C_ID”，“名称”分组，并使用以下命令创建“ MainRecord” case_when

library(dplyr)
df1 %>%
  group_by(C_ID, Name) %>%
  mutate(MainRecord = case_when(row_number()==1 ~ "X", TRUE ~ ""))
# A tibble: 6 x 3
# Groups:   C_ID, Name [3]
#   C_ID Name  MainRecord
#  <int> <chr> <chr>     
#1     1 JM    X         
#2     1 JM    ""        
#3     1 JM    ""        
#4     2 DM    X         
#5     3 TY    X         
#6     3 TY    ""        

或另一个选择是 ifelse

df1 %>%
   group_by(C_ID, Name) %>% 
   mutate(MainRecord = ifelse(row_number()==1, "X", ""))

或使用索引

df1 %>% 
   group_by(C_ID, Name) %>% 
   mutate(MainRecord = c("", "X")[(row_number()==1) + 1])

或使用data.table，使用来获取行索引，.I并分配（:=）与行相对应的'X'值

library(data.table)
i1 <- setDT(df1)[, .I[seq_len(.N) == 1], .(C_ID, Name)]$V1
df1[i1, MainRecord := "X"]

或搭配 base R

i1 <- with(df1, ave(seq_along(C_ID), C_ID, Name, FUN = seq_along)==1)
df1$MainRecord[i1] <- "X"