按组向原始数据添加一列均值 [英] Adding a column of means by group to original data

问题描述

我想根据 R data.frame 中的因子列添加一列均值.像这样:

I want to add a column of means based on factor column in R data.frame. Like this:

df1 <- data.frame(X = rep(x = LETTERS[1:2], each = 3), Y = 1:6)
df2 <- aggregate(data = df1, Y ~ X, FUN = mean)
df3 <- merge(x = df1, y = df2, by = "X", suffixes = c(".Old",".New"))
df3
#   X Y.Old Y.New
# 1 A     1     2
# 2 A     2     2
# 3 A     3     2
# 4 B     4     5
# 5 B     5     5
# 6 B     6     5

为了解决这个问题，我必须创建两个不必要的data.frames.我想知道一种通过因子列将平均值列附加到原始 data.frame 而不创建任何额外的 data.frames 的方法.感谢您的时间和帮助.

To accomplish this problem I've to create two unnecessary data.frames. I'd like to know a way to append a column of means by factor column into my original data.frame without creating any extra data.frames. Thanks for your time and help.

推荐答案

这就是 ave 函数的用途.

This is what the ave function is for.

df1$Y.New <- ave(df1$Y, df1$X)

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