Spread valued column into binary 'time series' in R - r

Question

I'm attempting to spread a valued column first into a set of binary columns and then gather them again in a 'time series' format.
By way of example, consider locations that have been conquered at certain times, with data that looks like this:
df1 <- data.frame(locationID = c(1,2,3), conquered_in = c(1931, 1932, 1929))
locationID conquered_in
1 1 1931
2 2 1932
3 3 1929
I'm attempting to reshape the data to look like this:
df2 <- data.frame(locationID = c(1,1,1,1,2,2,2,2,3,3,3,3), year = c(1929,1930,1931,1932,1929,1930,1931,1932,1929,1930,1931,1932), conquered = c(0,0,1,1,0,0,0,0,1,1,1,1))
locationID year conquered
1 1 1929 0
2 1 1930 0
3 1 1931 1
4 1 1932 1
5 2 1929 0
6 2 1930 0
7 2 1931 0
8 2 1932 0
9 3 1929 1
10 3 1930 1
11 3 1931 1
12 3 1932 1
My original strategy was to spread on conquered and then attempt a gather. This answer seemed close, but I can't seem to get it right with fill, since I'm trying to populate the later years with 1's also.

Answer 1

You can use complete() to expand the data frame and then use cumsum() when conquered equals 1 to fill the grouped data downwards.
library(tidyr)
library(dplyr)
df1 %>%
mutate(conquered = 1) %>%
complete(locationID, conquered_in = seq(min(conquered_in), max(conquered_in)), fill = list(conquered = 0)) %>%
group_by(locationID) %>%
mutate(conquered = cumsum(conquered == 1))
# A tibble: 12 x 3
# Groups: locationID [3]
locationID conquered_in conquered
<dbl> <dbl> <int>
1 1 1929 0
2 1 1930 0
3 1 1931 1
4 1 1932 1
5 2 1929 0
6 2 1930 0
7 2 1931 0
8 2 1932 1
9 3 1929 1
10 3 1930 1
11 3 1931 1
12 3 1932 1

Answer 2

Using complete from tidyr would be better choice. Though we need to aware that the conquered year may not fully cover all the year from beginning to end of the war.
library(dplyr)
library(tidyr)
library(magrittr)
df1 <- data.frame(locationID = c(1,2,3), conquered_in = c(1931, 1932, 1929))
# A data frame full of all year you want to cover
df2 <- data.frame(year=seq(1929, 1940, by=1))
# Create a data frame full of combination of year and location + conquered data
df3 <- full_join(df2, df1, by=c("year"="conquered_in")) %>%
mutate(conquered=if_else(!is.na(locationID), 1, 0)) %>%
complete(year, locationID) %>%
arrange(locationID) %>%
filter(!is.na(locationID))
# calculate conquered depend on the first year it get conquered - using group by location
df3 %<>%
group_by(locationID) %>%
# year 2000 in the min just for case if you have location that never conquered
mutate(conquered=if_else(year>=min(2000, year[conquered==1], na.rm=T), 1, 0)) %>%
ungroup()
df3 %>% filter(year<=1932)
# A tibble: 12 x 3
year locationID conquered
<dbl> <dbl> <dbl>
1 1929 1 0
2 1930 1 0
3 1931 1 1
4 1932 1 1
5 1929 2 0
6 1930 2 0
7 1931 2 0
8 1932 2 1
9 1929 3 1
10 1930 3 1
11 1931 3 1
12 1932 3 1