每个类别的年度总和

Question

我有一个数据农场，如下图所示。

Answer 1

使用data.table，将类似于：

library(data.table)
dat <- data.table(Year = c(2016, 2016, 2015), TF = c("Import", "Export", "Export"), value = c(123, 456, 789))
dat[, .(`total export` = sum(value[TF == "Export"]), `total import` = sum(value[TF == "Import"]), total = sum(value)), by = Year]