Repeat vector in a dataframe column but start at a given row

Question

I have a dataframe of country GDP and population from 2010 to 2100. I have leftjoined gdp growth for 3 years for each country(2020-2022). I would like to replicate these 3 years with a gap of NAs inbetween. I tried the following. It appeared to work, however on closer inspection it turned out that the sequence (NAs and 3 x GDP growth) started from 2010 but only appeared for the range that i required.

   DF<-DF%>%
      group_by(Country)%>%
      mutate(gdp_forecast=ifelse(Year>2022, rep(c(rep(NA, 2),gdp_forecast[!is.na(gdp_forecast)]), length.out=78), gdp_forecast))

This is an example of the current results.

structure(list(Country = c("Afghanistan", "Afghanistan", "Afghanistan", 
"Afghanistan", "Afghanistan", "Afghanistan", "Afghanistan", "Afghanistan", 
"Afghanistan", "Afghanistan", "Afghanistan", "Afghanistan", "Afghanistan", 
"Afghanistan", "Afghanistan", "Afghanistan", "Afghanistan", "Afghanistan", 
"Afghanistan", "Afghanistan"), gdp = c(15936.80064, 16873.912078, 
17811.023516, 18748.134954, 19685.246392, 20622.35783, 21648.660914, 
22674.963998, 23701.267082, 24727.570166, 25753.87325, 27258.147678, 
28762.422106, 30266.696534, 31770.970962, 33275.24539, 35342.146188, 
37409.046986, 39475.947784, 41542.848582), gdp_forecast = c(NA, 
NA, NA, NA, NA, NA, NA, NA, NA, NA, -5.5, 2.5, 3.3, NA, NA, NA, 
NA, NA, NA, NA), Year = c(2010, 2011, 2012, 2013, 2014, 2015, 
2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024, 2025, 2026, 
2027, 2028, 2029), gdp_forecast1 = c(NA, NA, NA, NA, NA, NA, 
NA, NA, NA, NA, NA, NA, NA, 2.5, 3.3, NA, NA, -5.5, 2.5, 3.3)), row.names = c(NA, 
-20L), groups = structure(list(Country = "Afghanistan", .rows = structure(list(
    1:20), ptype = integer(0), class = c("vctrs_list_of", "vctrs_vctr", 
"list"))), row.names = 1L, class = c("tbl_df", "tbl", "data.frame"
), .drop = TRUE), class = c("grouped_df", "tbl_df", "tbl", "data.frame"
))

This is the expected output

	Country	gdp	gdp_forecast	Year	gdp_forecast1
8	Afghanistan	22675.	NA	2017	NA
9	Afghanistan	23701.	NA	2018	NA
10	Afghanistan	24728.	NA	2019	NA
11	Afghanistan	25754.	-5.5	2020	NA
12	Afghanistan	27258.	2.5	2021	NA
13	Afghanistan	28762.	3.3	2022	NA
14	Afghanistan	30267.	NA	2023	NA
15	Afghanistan	31771.	NA	2024	NA
16	Afghanistan	33275.	NA	2025	-5.5
17	Afghanistan	35342.	NA	2026	2.5
18	Afghanistan	37409.	NA	2027	3.3
19	Afghanistan	39476.	NA	2028	NA
20	Afghanistan	41543.	NA	2029	NA

I have tried to include sufficient information to make this clear. — Aimen Sattar

akrun akrun · Accepted Answer · 2021-02-18T20:49:07

We can use rep with length.out

library(dplyr)
DF %>% 
   group_by(Country) %>% 
   mutate(gdp_forecast1 = NA_real_, 
   gdp_forecast1 = replace(gdp_forecast1, Year > 2022, 
      rep(c(NA, NA, gdp_forecast[!is.na(gdp_forecast)]), 
       length.out = sum(Year > 2022))))

-output

# A tibble: 20 x 5
# Groups:   Country [1]
   Country        gdp gdp_forecast  Year gdp_forecast1
   <chr>        <dbl>        <dbl> <dbl>         <dbl>
 1 Afghanistan 15937.         NA    2010          NA  
 2 Afghanistan 16874.         NA    2011          NA  
 3 Afghanistan 17811.         NA    2012          NA  
 4 Afghanistan 18748.         NA    2013          NA  
 5 Afghanistan 19685.         NA    2014          NA  
 6 Afghanistan 20622.         NA    2015          NA  
 7 Afghanistan 21649.         NA    2016          NA  
 8 Afghanistan 22675.         NA    2017          NA  
 9 Afghanistan 23701.         NA    2018          NA  
10 Afghanistan 24728.         NA    2019          NA  
11 Afghanistan 25754.         -5.5  2020          NA  
12 Afghanistan 27258.          2.5  2021          NA  
13 Afghanistan 28762.          3.3  2022          NA  
14 Afghanistan 30267.         NA    2023          NA  
15 Afghanistan 31771.         NA    2024          NA  
16 Afghanistan 33275.         NA    2025          -5.5
17 Afghanistan 35342.         NA    2026           2.5
18 Afghanistan 37409.         NA    2027           3.3
19 Afghanistan 39476.         NA    2028          NA  
20 Afghanistan 41543.         NA    2029          NA

Repeat vector in a dataframe column but start at a given row

1 Answers