Earliest Date for each id in R

Another answer that uses dplyr's filter command:

dta %>% 
  group_by(id) %>%
  filter(date == min(date))

You may use library(sqldf) to get the minimum date as follows:

data1<-data.frame(id=c("789","123","456","123","123","456","789"),
                  e_date=c("2016-05-01","2016-07-02","2016-08-25","2015-12-11","2014-03-01","2015-07-08","2015-12-11"))  

library(sqldf)
data2 = sqldf("SELECT id,
                    min(e_date) as 'earliest_date'
                    FROM data1 GROUP BY 1", method = "name__class")    

head(data2)   

id   earliest_date   
123    2014-03-01      
456    2015-07-08   
789    2015-12-11  

We can use data.table. Convert the 'data.frame' to 'data.table' (setDT(data_full)), grouped by 'id', we get the 1st row (head(.SD, 1L)).

library(data.table)
setDT(data_full)[order(e_date), head(.SD, 1L), by = id]

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Or using dplyr, after grouping by 'id', arrange the 'e_date' (assuming it is of Date class) and get the first row with slice.

library(dplyr)
data_full %>%
    group_by(id) %>%
    arrange(e_date) %>%
    slice(1L)

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If we need a base R option, ave can be used

data_full[with(data_full, ave(e_date, id, FUN = function(x) rank(x)==1)),]