Earliest Date for each id in R

Question

I have a dataset where each individual (id) has an e_date, and since each individual could have more than one e_date, I\'m trying to get the earli

Answer 1

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)),]