如何防止 ifelse() 将 Date 对象转换为数字对象 [英] How to prevent ifelse() from turning Date objects into numeric objects

问题描述

我正在使用函数 ifelse() 来操作日期向量.我希望结果是 Date 类，结果却意外地得到了一个 numeric 向量.下面是一个例子:

I am using the function ifelse() to manipulate a date vector. I expected the result to be of class Date, and was surprised to get a numeric vector instead. Here is an example:

dates <- as.Date(c('2011-01-01', '2011-01-02', '2011-01-03', '2011-01-04', '2011-01-05'))
dates <- ifelse(dates == '2011-01-01', dates - 1, dates)
str(dates)

这尤其令人惊讶，因为对整个向量执行操作返回一个 Date 对象.

This is especially surprising because performing the operation across the entire vector returns a Date object.

dates <- as.Date(c('2011-01-01', '2011-01-02', '2011-01-03', '2011-01-04','2011-01-05'))
dates <- dates - 1
str(dates)

我应该使用其他函数来操作 Date 向量吗?如果有，是什么功能?如果没有，我如何强制 ifelse 返回与输入相同类型的向量?

Should I be using some other function to operate on Date vectors? If so, what function? If not, how do I force ifelse to return a vector of the same type as the input?

ifelse 的帮助页面表明这是一项功能，而不是错误，但我仍在努力寻找对我发现的令人惊讶的行为的解释.

The help page for ifelse indicates that this is a feature, not a bug, but I'm still struggling to find an explanation for what I found to be surprising behavior.

推荐答案

您可以使用 data.table::fifelse (data.table >= 1.12.3) 或 dplyr::if_else.

You may use data.table::fifelse (data.table >= 1.12.3) or dplyr::if_else.

与 ifelse 不同，felse 保留输入的类型和类别.

Unlike ifelse, fifelse preserves the type and class of the inputs.

library(data.table)
dates <- fifelse(dates == '2011-01-01', dates - 1, dates)
str(dates)
# Date[1:5], format: "2010-12-31" "2011-01-02" "2011-01-03" "2011-01-04" "2011-01-05"

---

dplyr::if_else

来自 dplyr 0.5.0 发行说明:

[if_else] 具有比 ifelse() 更严格的语义:true 和 false 参数必须是同类型.这提供了一个不那么令人惊讶的返回类型，并保留了像 dates" 这样的 S3 向量..

[if_else] have stricter semantics that ifelse(): the true and false arguments must be the same type. This gives a less surprising return type, and preserves S3 vectors like dates" .

library(dplyr)
dates <- if_else(dates == '2011-01-01', dates - 1, dates)
str(dates)
# Date[1:5], format: "2010-12-31" "2011-01-02" "2011-01-03" "2011-01-04" "2011-01-05" 

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