根据条件删除R中的重复项

Question

I need to embed a condition in a remove duplicates function. I am working with large student database from South Africa, a highly multilingual country. Last week you guys gave me the code to remove duplicates caused by retakes, but I now realise my language exam data shows some students offering more than 2 different languages. The source data, simplified looks like this

STUDID   MATSUBJ     SCORE
101      AFRIKAANSB   1
101      AFRIKAANSB   4
102      ENGLISHB     2
102      ISIZULUB     7
102      ENGLISHB     5

The result file I need is

STUDID   MATSUBJ    SCORE  flagextra
101      AFRIKAANS   4
102      ENGLISH     5
102      ISIZULUB    7     1

I need to flag the extra language so that I can see what languages they are and make new category for this

Answer 1

May be this helps

library(tidyverse)
df1 %>% 
   group_by(STUDID, MATSUBJ) %>% 
   summarise(SCORE = max(SCORE), 
             flagextra = as.integer(!sum(duplicated(MATSUBJ))))
# A tibble: 3 x 4
# Groups:   STUDID [?]
#  STUDID MATSUBJ    SCORE flagextra
#   <int> <chr>      <dbl>     <int>
#1    101 AFRIKAANSB     4         0
#2    102 ENGLISHB       5         0
#3    102 ISIZULUB       7         1

---

Or with base R

i1 <- !(duplicated(df1[1:2])|duplicated(df1[1:2], fromLast = TRUE))
transform(aggregate(SCORE ~ ., df1, max), 
          flagextra = as.integer(MATSUBJ %in% df1$MATSUBJ[i1]))

data

df1 <- structure(list(STUDID = c(101L, 101L, 102L, 102L, 102L), MATSUBJ 
      = c("AFRIKAANSB", 
 "AFRIKAANSB", "ENGLISHB", "ISIZULUB", "ENGLISHB"), SCORE = c(1L, 
 4L, 2L, 7L, 5L)), class = "data.frame", row.names = c(NA, -5L
 ))

Answer 2

Two stage procedure works better for me as a newbie to R:

remove the duplicates caused by subject retakes df<-LANGSEC%>%group_by (STUDID,MATRICSUBJ) %>%top_n(1,SUBJSCORE) #Then flag one of the two subjects causing the remaining duplicates LANGSEC$flagextra<-as.integer(duplicated(LANGSEC$STUDID),LANGSEC$MATRICSUBJ # Then filter for this third language and make new file LANG3<-LANGSEC%>% filter (flagextra==1) #Then remove these from the other file LANG2<-LANGSEC %>% filter (!flagextra==1)