如何在R语言数据框中保留每个ID的首次出现并新增唯一ID标识变量

First, let's start with your sample data frame so everyone can follow along:

df <- structure(list(
  ID = c("Jerry", "Jerry", "Mary", "Tom"), 
  Score = c(65, 98, 88, 75)
), row.names = c(NA, -4L), class = c("tbl_df", "tbl", "data.frame"))

1. Keep only the first occurrence of each ID #

There are a couple of straightforward ways to do this with tidyverse tools (since your data is a tibble, this fits perfectly):

Method 1: Using distinct() #

The distinct() function lets you keep unique rows for a specified column, and .keep_all = TRUE ensures we retain all other columns in the row:

library(dplyr)

df_first_occurrence <- df %>%
  distinct(ID, .keep_all = TRUE)

# Result:
# # A tibble: 3 × 2
#   ID    Score
#   <chr> <dbl>
# 1 Jerry    65
# 2 Mary     88
# 3 Tom      75

Method 2: Using group_by() + slice_head() #

Group by the ID column, then take the first row of each group:

df_first_occurrence <- df %>%
  group_by(ID) %>%
  slice_head(n = 1) %>%
  ungroup() # Don't forget to ungroup if you don't need the grouping anymore

This gives the exact same result as the first method.

2. Add a UniqueID column showing ID only on its first occurrence #

We can use row_number() within each group to check if a row is the first occurrence, then populate UniqueID accordingly. Here's how:

df_with_uniqueid <- df %>%
  group_by(ID) %>%
  mutate(UniqueID = ifelse(row_number() == 1, ID, NA_character_)) %>%
  ungroup()

# Result:
# # A tibble: 4 × 3
#   ID    Score UniqueID
#   <chr> <dbl> <chr>   
# 1 Jerry    65 Jerry   
# 2 Jerry    98 NA      
# 3 Mary     88 Mary    
# 4 Tom      75 Tom     

Alternatively, if you prefer not to use grouping, you can use the duplicated() function directly:

df_with_uniqueid <- df %>%
  mutate(UniqueID = ifelse(!duplicated(ID), ID, NA_character_))

This works because duplicated(ID) returns FALSE for the first occurrence of each ID, so !duplicated(ID) is TRUE exactly when we want to show the ID.

内容的提问来源于stack exchange，提问作者Stataq