选择具有多个不同值的组 [英] Select groups with more than one distinct value

问题描述

我有包含分组变量(来自")和值(数字")的数据:

I have data with a grouping variable ("from") and values ("number"):

from number
   1      1
   1      1
   2      1
   2      2
   3      2
   3      2

我想对数据进行子集化并选择具有两个或多个唯一值的组.在我的数据中，只有第 2 组有多个不同的数字"，因此这是所需的结果:

I want to subset the data and select groups which have two or more unique values. In my data, only group 2 has more than one distinct 'number', so this is the desired result:

from number
   2      1
   2      2

推荐答案

几种可能性，这是我最喜欢的

Several possibilities, here's my favorite

library(data.table)
setDT(df)[, if(+var(number)) .SD, by = from]
#    from number
# 1:    2      1
# 2:    2      2

基本上，每个组我们都会检查是否有任何差异，如果TRUE，则返回组值

Basically, per each group we are checking if there is any variance, if TRUE, then return the group values

使用基础 R，我会选择

With base R, I would go with

df[as.logical(with(df, ave(number, from, FUN = var))), ]
#   from number
# 3    2      1
# 4    2      2

<小时>

编辑:对于非数字数据，您可以为 data.table 的开发版本(或使用 length(unique(number)) > 1 代替

---

Edit: for a non numerical data you could try the new uniqueN function for the devel version of data.table (or use length(unique(number)) > 1 instead

setDT(df)[, if(uniqueN(number) > 1) .SD, by = from]

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