根据逻辑条件在行的子集上对数据帧进行子集 [英] Subsetting a data frame based on a logical condition on a subset of rows

问题描述

我试图提出一种解决Followig问题的简单方法.这是最小的工作示例:

I've tried to come up with a simple solution to the followig problem. Here is the minimum working example:

data <- data.frame(subject = c('Math', 'English', 'French', 'English'),
                   grade = c(1, 3, 5, 4))

我想要一个比较Enlish成绩并返回逻辑矢量的函数，该逻辑矢量对于英语成绩最高的行为TRUE，对于所有其他行为FALSE.在这种情况下， [1]否否否是.

I want a function that compares Enlish grades and returns a logical vector that has TRUE for the row with the highest english grade, and FALSE for all other rows. In this case [1] FALSE FALSE FALSE TRUE.

推荐答案

我们可以通过 ave 与成绩"以获取逻辑索引，并检查主题"是否也为英语"

We can get the max 'grade' per 'subject' with ave compare it with the 'grade' to get a logical index and check whether the 'subject' is also 'English'

with(data, ave(grade, subject, FUN = max)==grade & subject == "English") 
#[1] FALSE FALSE FALSE  TRUE

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