Expand ranges defined by “from” and “to” columns

Question

I have a data frame containing \"name\" of U.S. Presidents, the years when they start and end in office, (\"from\" and \"to\" columns

Answer 1

Another solution using dplyr and tidyr:

library(magrittr) # for pipes
df <- data.frame(tata = c('toto1', 'toto2'), from = c(2000, 2004), to = c(2001, 2009))

#    tata from   to
# 1 toto1 2000 2001
# 2 toto2 2004 2009

df %>% 
  dplyr::as.tbl() %>%
  dplyr::rowwise() %>%
  dplyr::mutate(combined = list(seq(from, to))) %>%
  dplyr::select(-from, -to) %>%
  tidyr::unnest(combined)

#   tata  combined
#   <fct>    <int>
# 1 toto1     2000
# 2 toto1     2001
# 3 toto2     2004
# 4 toto2     2005
# 5 toto2     2006
# 6 toto2     2007
# 7 toto2     2008
# 8 toto2     2009

Answer 2

An alternate tidyverse approach using unnest and map2.

library(tidyverse)

presidents %>%
  unnest(year = map2(from, to, seq)) %>%
  select(-from, -to)

#              name  year
# 1    Bill Clinton  1993
# 2    Bill Clinton  1994
...
# 21   Barack Obama  2011
# 22   Barack Obama  2012

Edit: From tidyr v1.0.0 new variables can no longer be created as part of unnest().

presidents %>%
  mutate(year = map2(from, to, seq)) %>%
  unnest(year) %>%
  select(-from, -to)

Answer 3

Use by to create a by list L of data.frames, one data.frame per president, and then rbind them together. No packages are used.

L <- by(presidents, presidents$name, with, data.frame(name, year = from:to))
do.call("rbind", setNames(L, NULL))

If you don't mind row names then the last line could be reduced to just:

do.call("rbind", L)