Remove duplicated rows by ID in R data.table, but add a new column with the concatenated dates from another column

Question

I have a large data table of patient data. I want to delete rows where "id" is duplicated without losing the information in the "date" column.

id  date
01  2004-07-01
02  NA
03  2013-11-15
03  2005-03-15
04  NA
05  2011-07-01
05  2012-07-01

I could do this one of two ways -

1. create a column that writes over the date column values to concatenate all the dates for that ID, ie:

    id date_new 01 2004-07-01 02 NA 03 2013-11-15; 2005-03-15 04 NA 05 2011-07-01; 2012-07-01 

or

2. create one new column for each additional date, ie:

    id date_new date_new2 01 2004-07-01 NA 02 NA NA 03 2013-11-15 2005-03-15 04 NA NA 05 2011-07-01 2012-07-01 

I have tried a few things, but they keep crashing my R session (I get the message R Session Aborted. R encountered a fatal error. The session was terminated. ):

setkey(DT, "id")
unique_DT <- subset(unique(DT))

and:

DT[!duplicated(DT[, "id", with = FALSE])]

However, besides crashing R, neither of these solutions does what I want with the dates.

Any ideas? I am new to data table (and R generally) but I have the vague sense that I could solve this with := somehow.

Answer 1

尝试这个：

dt[,c(date_new=paste(date,collapse="; "),.SD),by=id]

Answer 2

You can use the aggregate function and it should do what you want. I was having some trouble with the dates switching to factors, but it seems like enclosing the date string with I() keeps it as a character.

id=c(1,2,3,3,4,5,5)
date = c("2004-07-01","NA","2013-11-15","2005-03-15","NA",
         "2011-07-01","2012-07-01")
data=as.data.frame(list(id=id,date=date))

data$date=as.character(data$date)

aggregate(list(date = I(data$date)),by=list(id = data$id),c)

  id                   date
1  1             2004-07-01
2  2                     NA
3  3 2013-11-15, 2005-03-15
4  4                     NA
5  5 2011-07-01, 2012-07-01

edit: used the aggregate function but used paste instead of c. Changing the collapse option to ";" should solve the separator problem

newdata = aggregate(list(date = I(data$date)),
                    by=list(id = data$id),
                    function(x){paste(unique(x),collapse=";")})
newdata


  id                  date
1  1            2004-07-01
2  2                    NA
3  3 2013-11-15;2005-03-15
4  4                    NA
5  5 2011-07-01;2012-07-01