如何对data.table中满足某些最低条件的行进行子集？ [英] How do I subset rows in data.table that meet some minimum criteria?

问题描述

我是R中的data.table的noob，我想在此示例中跳过z = 3的最后一个值：

I'm a noob to data.table in R and I'd like to skip the last value of z=3 in this example:

> DT = data.table(y=c(1,1,2,2,2,3,3,3,4,4),x=1:10,z=c(1,1,1,1,2,2,2,2,3,3))
> DT[,list(list(predict(smooth.spline(x,y),c(4,5,6))$y)),by=z]

Error in smooth.spline(x, y) : need at least four unique 'x' values

我得到我想要的答案：

> DT = data.table(y=c(1,1,2,2,2,3,3,3),x=1:8,z=c(1,1,1,1,2,2,2,2))
> DT[,list(list(predict(smooth.spline(x,y),c(4,5,6))$y)),by=z]

   z                                                  V1
1: 1  2.09999998977689,2.49999997903384,2.89999996829078
2: 2 0.999895853971133,2.04533519691888,2.90932467439562

伟大的包！

推荐答案

省略 z / p>

Omitting the rows were z is 3 is as simple as

DT[z!=3,  <whatever expression you'd like>]

如果您的数据表以 z 为键，那么您可以使用

If your data.table is keyed by z then you can use

DT[!.(3), .....]

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