Creating new variable by focusing range of other variables

I want to create a variable that include all numbers between (startyear) and (endyear – 1). My data looks like this:

I want to show my data like this:

I have many countries in data set. I want to manipulate all data set with "the" code.

>Solution :

We may get the sequence (:) by row and unnest the list column

library(dplyr)
library(purrr)
library(tidyr)
df1 %>%
   mutate(year = map2(startyear, endyear-1, `:`)) %>%
   unnest(year)

-output

# A tibble: 10 × 5
   country leader     startyear endyear  year
   <chr>   <chr>          <int>   <int> <int>
 1 US      Eisenhower      1953    1961  1953
 2 US      Eisenhower      1953    1961  1954
 3 US      Eisenhower      1953    1961  1955
 4 US      Eisenhower      1953    1961  1956
 5 US      Eisenhower      1953    1961  1957
 6 US      Eisenhower      1953    1961  1958
 7 US      Eisenhower      1953    1961  1959
 8 US      Eisenhower      1953    1961  1960
 9 US      Kennedy         1961    1963  1961
10 US      Kennedy         1961    1963  1962

data

df1 <- structure(list(country = c("US", "US"), leader = c("Eisenhower", 
"Kennedy"), startyear = c(1953L, 1961L), endyear = c(1961L, 1963L
)), class = "data.frame", row.names = c(NA, -2L))