如何在R数据表中的特定列之后选择组后的行的子集 [英] How do I select a subset of rows after group by a specific column in R Data table

问题描述

我想根据R数据表中特定列分组后的条件来选择行的子集。
以Mtcars数据为例。

I want to select a subset of rows based upon a condition after grouping by a specific column in R data table . Take Mtcars data for an example .

dt_mtcars <- as.data.table(mtcars)


dt_mtcars[,.N,by=.(hp)]

    hp  N
 1: 110 3
 2:  93 1
 3: 175 3
 4: 105 1
 5: 245 2
 6:  62 1
 7:  95 1
 8: 123 2
 9: 180 3
10: 205 1
11: 215 1
12: 230 1
13:  66 2
14:  52 1
15:  65 1
16:  97 1
17: 150 2
18:  91 1
19: 113 1
20: 264 1
21: 335 1
22: 109 1
     hp N

就像选择一个子集合的数据基于计数为eg在这里我想有所有的数据在dt_mtcars其中N> 1
如果我尝试这样的东西（这在概念上是我想要实现的）它显示所有行，而不是获得N大于1的行。

Now what I am trying to achieve is like selecting a sub set of data based on the count for e.g in here I want to have all the data in dt_mtcars where N >1 if I try something like this (which is conceptually what I am trying to achieve) it shows all the rows rather than getting the rows where N is greater than 1 .

dt_mtcars[.N>1,.SD,by=.(hp)]

请协助。

推荐答案

我们可以使用如果

dt_mtcars[, if(.N>1) .SD ,hp]

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