This is what I understand from your description
library(dplyr)
df <- data.frame(
stringsAsFactors = FALSE,
years = c(2008,2009,2011,2012,2013,
2014,2015,2008,2009,2010,2012,2015),
Names = c("A","A","A","A","A","A",
"A","B","B","B","B","B"),
Variable1 = c(1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1),
Dummy_variable = c(1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 1, 1)
)
df %>%
group_by(Names) %>%
mutate(Dummy_variable = as.numeric(length(unique(Variable1)) == 1))
#> # A tibble: 12 x 4
#> # Groups: Names [2]
#> years Names Variable1 Dummy_variable
#> <dbl> <chr> <dbl> <dbl>
#> 1 2008 A 1 1
#> 2 2009 A 1 1
#> 3 2011 A 1 1
#> 4 2012 A 1 1
#> 5 2013 A 1 1
#> 6 2014 A 1 1
#> 7 2015 A 1 1
#> 8 2008 B 0 0
#> 9 2009 B 1 0
#> 10 2010 B 0 0
#> 11 2012 B 1 0
#> 12 2015 B 1 0
Created on 2021-03-28 by the reprex package (v1.0.0.9002)