Here is an example how to obtain (in vector urate) the values of the variable unemployment_rate
> library(jsonlite)
> fb <- "https://github.com/iancoleman/cia_world_factbook_api/raw/master/data/factbook.json"
> J <- fromJSON(readLines(fb))
> C <- names(J$countries)
> head(C)
[1] "world" "afghanistan" "akrotiri" "albania"
[5] "algeria" "american_samoa"
> n <- length(C)
> urate <- rep(0,n)
> for(ci in 1:n){
+ ur <- J$countries[[ci]]$data$economy$unemployment_rate$annual_values
+ v <- ur$value[1]; d <- ur$date[1]
+ urate[ci] <- ifelse(is.null(v),NA,v)
+ year <- ifelse(is.null(d),"0000",d)
+ cat("U_rate:",format(ci,width=3,justify="r"),
+ format(urate[ci],width=7,nsmall=2),year,C[ci],"\n")
+ }
U_rate: 1 7.70 2017 world
U_rate: 2 23.90 2017 afghanistan
U_rate: 3 NA 0000 akrotiri
U_rate: 4 5.83 2019 albania
U_rate: 5 11.70 2017 algeria
U_rate: 6 29.80 2005 american_samoa
U_rate: 7 3.70 2016 andorra
U_rate: 8 6.60 2016 angola
...
U_rate: 257 15.00 2008 zambia
U_rate: 258 11.30 2014 zimbabwe
U_rate: 259 8.60 2016 european_union
>
For some countries, we get values for different years. In the example, we are using the most recent value. You could use some more complicated selection of value - for example, the closest to the year 2017.
Here is another example for variable contraceptive_prevalence_rate
> crate <- rep(0,n)
> for(ci in 1:n){
+ cr <- J$countries[[ci]]$data$people$contraceptive_prevalence_rate
+ v1 <- cr$value[1]
+ u <- cr$units[1]
+ d1 <- cr$date[1]
+ crate[ci] <- ifelse(is.null(v1),NA,v1)
+ year <- ifelse(is.null(d1),"0000",d1)
+ cat("C_rate:",format(ci,width=3,justify="r"),
+ format(crate[ci],width=7,nsmall=2),year,C[ci],"\n")
+ }
C_rate: 1 NA 0000 world
C_rate: 2 18.90 2018 afghanistan
C_rate: 3 NA 0000 akrotiri
C_rate: 4 46.00 2017 albania
C_rate: 5 57.10 2012 algeria
...
C_rate: 255 NA 0000 western_sahara
C_rate: 256 33.50 2013 yemen
C_rate: 257 49.50 2018 zambia
C_rate: 258 66.80 2015 zimbabwe
C_rate: 259 NA 0000 european_union
>
It is not a very good variable - it contains many NAs. Try to avoid such variables in your project.