选择具有至少一个特定值的组 [英] Select groups which have at least one of a certain value

问题描述

如何根据各行上的条件选择组，例如，使包含至少一个(任意)的特定值的所有组保持不变，例如4(或任何其他至少满足 TRUE 的条件).或反过来说:如果组 not 中没有任何行，且条件为true，则应删除整个组.

How to select groups based on a condition on the individual rows, say keep all groups that contain at least one (ANY) of a certain value, e.g. 4, (or any other condition that is TRUE at least once). Or phrased the other way around: if a group does not have any rows where condition is true, the entire group should be removed.

让我们采用一个非常简单的数据，分为两个组，我想选择具有至少一行且 Value 为4的组(即组 B 此处)

Let's take a very simple data, with two groups, and I want to select the group that has at least one row with a Value of 4, (i.e. group B here)

library(dplyr)
df <- data.frame(Group = LETTERS[c(1,1,1,2,2,2)], Value=c(1:5, 4))

df
#   Group Value
# 1     A     1 # Group A has no values == 4 ~~> remove entire group 
# 2     A     2
# 3     B     3
# 4     B     4 # Group B has at least one 4 ~~> keep the whole group

先执行 group_by()，然后执行 filter (如

Doing group_by() and then filter (as in this post) will only select individual rows that contains a value of 4, not the whole group:

df %>%
  group_by(Group) %>%
  filter(Value == 4)
#    Group Value
#   <fctr> <int>
# 1      B     4

推荐答案

事实证明这很容易:您只需要在 filter 中使用 any()函数调用.确实，看来:

This turns out to be pretty easy: you just need to use the any() function in the filter call. Indeed, it appears that:

• filter(any(...))在 group_by()级别

filter(...)也会在 rowwise()级别上求值.

因此使用:

 df %>%
    group_by(Group) %>%
    filter(any(Value==4)) 

Group Value
 <fctr> <int>
1      B     3
2      B     4

有趣的是，同样出现在mutate上，比较:

Interestingly, the same appear with mutate, compare:

df %>%
group_by(Group) %>%
mutate(check1=any(Value==4), 
       check2=Value==4) 

   Group Value check1 check2
  <fctr> <int>  <lgl>  <lgl>
1      A     1  FALSE  FALSE
2      A     2  FALSE  FALSE
3      B     3   TRUE  FALSE
4      B     4   TRUE   TRUE

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