## example from the world bank
x <- data.frame(age=as.factor(c(
"0-4",
"5-9","10-14","15-19", "20-24",
"25-29","30-34","35-39","40-44","45-49",
"50-54","55-59","60-64","65-69","77-74","75-79","80+"
)),
pop=c(1971990, 2095820,2157190, 2094110,2116580, 2003840, 1785690,
1502990, 1214170, 796934, 627551, 530305, 488014,
364498, 259029,158047, 125941)
)
s <- sprague(x[,2])
s
all.equal(sum(s), sum(x[,2]))
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