I want to know for each country, the maximum sum of duration of primary,middle and high school(because for each year, the duration may not be the same). I firstly group_by country, and the use colSum, but the value I got was the max(colSum) for all, which means the group_bu does not work here at all.I want to know for each country, the maximum su
阅读背景：
为什么group_by不能在dplyr中使用max（colSums）
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