替换R数据帧中除1行以外的重复值 [英] Replacing the duplicate values except 1 row in R dataframe

问题描述

如何根据ID将R数据帧的特定列的重复值替换为NA（第一行除外）。举一个例子：

How can I replace the duplicated values of a specific column of R dataframe to NA (except the first row) based on ID. To give an example:

x <- data.frame(id=c("p1","p1","p1","p2","p2"),date=c("d1","d1","d1","d2","d2"))

并应导致以下结果：

x2 <- data.frame(id=c("p1","p1","p1","p2","p2"),date=c("d1","NA","NA","d2","NA"))

我必须维护每个id的多行数据结构，根本不用希望将日期值重复一次。

I have to maintain the data structure of multiple rows per id, simply do not want the date values to be repeated but once.

谢谢

推荐答案

选项1：基本的R方法是使用 ave（）将重复的 date 值替换为 NA ，每个 id 。

Option 1: A base R method is to use ave() replace the duplicated date values with NA for each group in id.

x$date <- ave(
    x$date, 
    x$id, 
    FUN = function(a) replace(a, duplicated(a), NA_integer_)
)

给出更新的 x 数据

  id date
1 p1   d1
2 p1 <NA>
3 p1 <NA>
4 p2   d2
5 p2 <NA>

上述方法适用于<$ c $中的多个值c> date ，将重复项替换为 NA 。如果仅是第一个组值，则可以使用上面或下面的代码，这可能会更快。

The method above will work for multiple values in date, replacing duplicates with NA. If it's only the first group value you're after, you could use the code above or the following, which may be faster.

ave(
    x$date,
    x$id,
    FUN = function(a) c(a[1], a[-1][NA])
)

此代码获取每个组中的第一个值，并用 NA 。尚不清楚您要哪个，因为示例数据每个 id 组只有一个值。

This code takes the first value in each group and replaces all the rest with NA. It's not clear which one you want, since your example data only has one value per id group.

选项2：使用 data.table 包的替代方法。由于 NA 是合乎逻辑的，因此 date [NA] 只是将值转换为 NA ，而不更改数据类型。

Option 2: An alternative using the data.table package. Since NA is logical, date[NA] simply turns values into NA without changing the type of the data.

library(data.table)
setDT(x)[duplicated(date), date := date[NA], by = id]

p>

which gives

   id date
1: p1   d1
2: p1   NA
3: p1   NA
4: p2   d2
5: p2   NA

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