Creating a Variable Initial Values from a base variable in Panel Data Structure in R

user_13356687 0
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I'm trying to create a new variable in R containing the initial values of another variable (crime) based on groups (countries) considering the initial period of time observable per group (on panel data framework), my current data looks like this:

country year Crime
Albania 2016 2.7369478
Albania 2017 2.0109779
Argentina 2002 9.474084
Argentina 2003 7.7898825
Argentina 2004 6.0739941

And I want it to look like this:

country year Crime Initial_Crime
Albania 2016 2.7369478 2.7369478
Albania 2017 2.0109779 2.7369478
Argentina 2002 9.474084 9.474084
Argentina 2003 7.7898825 9.474084
Argentina 2004 6.0739941 9.474084

I saw that ddply could make it work this way, but the problem is that it is not longer supported by the latest R updates.

Thank you in advance.

transform r panel
3 Answers
library(data.table)

setDT(data)[, Initial_Crime:=.SD[1,Crime], by=country]

     country year    Crime Initial_Crime
1:   Albania 2016 2.736948      2.736948
2:   Albania 2017 2.010978      2.736948
3: Argentina 2002 9.474084      9.474084
4: Argentina 2003 7.789883      9.474084
5: Argentina 2004 6.073994      9.474084
user_44475400

Maybe arrange by year, then after grouping by country set Initial_Crime to be the first Crime in the group.

library(tidyverse)

df %>%
  arrange(year) %>%
  group_by(country) %>%
  mutate(Initial_Crime = first(Crime))

Output

  country    year Crime Initial_Crime
  <chr>     <int> <dbl>         <dbl>
1 Argentina  2002  9.47          9.47
2 Argentina  2003  7.79          9.47
3 Argentina  2004  6.07          9.47
4 Albania    2016  2.74          2.74
5 Albania    2017  2.01          2.74
user_34606700

A data.table solution

setDT(df)

df[, x := 1:.N, country
   ][x==1, initial_crime := crime
     ][, initial_crime := nafill(initial_crime, type = "locf")
       ][, x := NULL
         ]
user_70138960
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