根据条件更新R数据框列

Question

I am trying to update a dataframe based on a certain condition. Here is the sample dataframe.

  fname mname lname
 1   RONALD D VALE
 2   RONALD  VALE
 3   JACK A SMITH
 4   JACK B SMITH
 5   JACK  SMITH

I would like to update the middle names column if the first and last names match. In this example, I would expect the following output.

  fname mname lname
 1   RONALD D VALE
 2   RONALD D VALE
 3   JACK A SMITH
 4   JACK B SMITH
 5   JACK  SMITH

I also do not want to update the table if there are two different middle initials. There are some missing values in the data. So the main aim is to identify and merge multiple entries which are possibly similar. At the same time, we do not want to introduce erroneous data into the table.

Answer 1

A tidyverse solution:

df %>% 
  group_by(fname, lname) %>% 
  mutate(mname_count = n_distinct(mname, na.rm = TRUE)) %>%
  mutate(mname = ifelse(mname_count == 1, unique(na.omit(mname)), mname)) %>%
  select(-mname_count)

Answer 2

An ugly base R solution (assuming you changed your "" to NA ):

unic<-unique(lolz[,c("fname","lname")])

for (i in 1:nrow(unic)){
  lelz<-lolz[lolz[,"fname"]==unic[i,1] & lolz[,"lname"]==unic[i,2],]$mnam
  if (sum(!is.na(lelz))==1){
    lelz[is.na(lelz)] <- "D"
    lolz[lolz[,"fname"]==unic[i,1] & lolz[,"lname"]==unic[i,2],][,2]<-lelz
  }
}

Answer 3

We can use data.table

library(data.table)
setDT(df1)[, mname := if(uniqueN(mname[nzchar(mname)])==1) 
                           mname[nzchar(mname)] else mname, .(fname,  lname)]
df1
#    fname mname lname
#1: RONALD     D  VALE
#2: RONALD     D  VALE
#3:   JACK     A SMITH
#4:   JACK     B SMITH
#5:   JACK       SMITH

data

df1 <- structure(list(fname = c("RONALD", "RONALD", "JACK", "JACK", 
 "JACK"), mname = c("D", "", "A", "B", ""), lname = c("VALE", 
 "VALE", "SMITH", "SMITH", "SMITH")), .Names = c("fname", "mname", 
 "lname"), class = "data.frame", row.names = c("1", "2", "3", 
 "4", "5"))