How to repeat observations n times in R?

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I am working on incorporating a variable that is recorded once per unit to a yearly dataset. While it is quite straightforward to repeat the observations n times, I have trouble assigning years to the observations.

The structure of my data is as follows:

id startyear endyear dummy
1  1946      2005    1
2  1957      2005    1
3  1982      2005    1
4  1973      2005    1

What I want to do is to create a new row, called years, which repeats unit 1 n = 2005 - 1946 = 59 times; unit 2 2005-1957 times, and so forth as well as assigning the year, generating the following output: 

id startyear endyear dummy year
1  1946      2005    1     1946
1  1946      2005    1     1947
1  1946      2005    1     1948
1  1946      2005    1     1949
[…]

I have attempted to use slice and mutate in dplyr, in combination with rep and seq but neither gives me the result I want. Any help would be greatly appreciated.

dplyr repeat r
2 Answers

We can use map2 to create a sequence from 'startyear' to 'endyear' for each element into a list and then unnest

library(tidyverse)
df1 %>% 
    mutate(year = map2(startyear, endyear, `:`)) %>%
    unnest
# id startyear endyear dummy year
#1    1      1946    2005     1 1946
#2    1      1946    2005     1 1947
#3    1      1946    2005     1 1948
#4    1      1946    2005     1 1949
#5    1      1946    2005     1 1950
#6    1      1946    2005     1 1951
#7    1      1946    2005     1 1952
#...

Or do a group by 'id', mutate into a list and unnest

df1 %>% 
  group_by(id) %>% 
  mutate(year = list(startyear:endyear)) %>% 
  unnest
user_37322710

Less elegant alternative, almost as simple:

library(tidyverse)
df1 %>% 
    uncount(endyear - startyear + 1, .id = "row") %>%
    mutate(year = startyear + row - 1)
user_68518250
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