我有一个data.table，我需要添加额外的列，它是标签 == 1 和标签 == 2 之间的比率，用于相同的 cID。我有可以做到这一点的代码，但结果是根据唯一“l”的数量减少的形式。但我需要一个包含重复项的完整列表。有什么建议么？提前致谢！
x y l cID
0.03588851 0.081635056 1 1
0.952514891 0.82677373 1 1
0.722920691 0.687278396 1 1
0.772207687 0.743329599 2 1
0.682710551 0.946685728 1 2
0.795816439 0.024320077 2 2
0.50788885 0.106910923 2 2
0.145871035 0.802771467 2 2
0.092942384 0.335054397 1 3
0.439765866 0.199329139 1 4
重现
x = c(0.03588851,0.952514891,0.722920691,0.772207687,0.682710551,0.795816439,0.50788885,0.145871035,0.092942384,0.439765866)
y = c(0.081635056,0.82677373,0.687278396,0.743329599,0.946685728,0.024320077,0.106910923,0.802771467,0.335054397,0.199329139)
l = c(1,1,1,2,1,2,2,2,1,1)
cID = c(1,1,1,1,2,2,2,2,3,4)
dt <- data.table(x,y,l,cID)
dt[,sum(l == 1)/sum(l == 2), by = cID]
我需要获得看起来像这样的比率列
x y l cID ratio
0.03588851 0.081635056 1 1 3
0.952514891 0.82677373 1 1 3
0.722920691 0.687278396 1 1 3
0.772207687 0.743329599 2 1 3
0.682710551 0.946685728 1 2 0.333333333
0.795816439 0.024320077 2 2 0.333333333
0.50788885 0.106910923 2 2 0.333333333
0.145871035 0.802771467 2 2 0.333333333
0.092942384 0.335054397 1 3 Inf
0.439765866 0.199329139 1 4 Inf