从R中的不同列汇总具有相同ID的值

Question

我的数据集有时包含同一年的多个观察结果。

    id          country ccode year  region   protest protestnumber  duration
    201990001   Canada  20  1990    North America   1   1   1
    201990002   Canada  20  1990    North America   1   2   1
    201990003   Canada  20  1990    North America   1   3   1
    201990004   Canada  20  1990    North America   1   4   57
    201990005   Canada  20  1990    North America   1   5   2
    201990006   Canada  20  1990    North America   1   6   1
    201991001   Canada  20  1991    North America   1   1   8
    201991002   Canada  20  1991    North America   1   2   5
    201992001   Canada  20  1992    North America   1   1   2
    201993001   Canada  20  1993    North America   1   1   1
    201993002   Canada  20  1993    North America   1   2   62
    201994001   Canada  20  1994    North America   1   1   1
    201994002   Canada  20  1994    North America   1   2   1
    201995001   Canada  20  1995    North America   1   1   1
    201995002   Canada  20  1995    North America   1   2   1
    201996001   Canada  20  1996    North America   1   1   1
    201997001   Canada  20  1997    North America   1   1   13
    201997002   Canada  20  1997    North America   1   2   16

我需要将同一年的所有价值总和为每年一个值。因此，我每列都会收到一个值。我希望在所有年份和国家的整个数据集中进行迭代。任何帮助深表感谢。谢谢！