R如何有条件地替换变量的值 [英] R How to replace value of a variable conditionally

问题描述

我确定这个问题已经被问到了一堆时间，但我找不到解决方案。

I am sure this question has been asked stacks of time but I couldn't find a solution.

我试图有条件地替换第二个变量的值基于第一个变量的值。这是数据。

I am trying to conditionally replace the value of a second variable based on the value of first variable. Here is the data.

 MAKE Continent
1  HOLDEN        US
2  HOLDEN        US
3    FORD        US
4    FORD        US

if(gsample$MAKE == "HOLDEN") gsample$Continent = "AUS"

警告信息：

In if (gsample$MAKE == "HOLDEN") gsample$Continent = "AUS" :
  the condition has length > 1 and only the first element will be used

推荐答案

基于逻辑条件 MAKE =='HOLDEN'，如果条件为<，我们使用 ifelse 返回'AUS' code> TRUE 或者返回'Continent'的相应值。

Based on the logical condition MAKE=='HOLDEN', we use ifelse to return 'AUS' if that the condition is TRUE or else return the corresponding values of 'Continent'.

gsample$Continent <- with(gsample, ifelse(MAKE=='HOLDEN', 'AUS', Continent))

或者我们使用逻辑索引对大陆进行子集化并通过分配来替换它。

Or we use the logical index to subset the 'Continent' and replace that by assigning.

gsample$Continent[gsample$MAKE=='HOLDEN'] <- 'AUS'

或者我们可以使用 data.table 。我们根据 i setDT（gsample）） c $ c>，我们将（：= ）大陆分配给'AUS'

Or we can use data.table. We convert the 'data.frame' to 'data.table' (setDT(gsample)), based on the logical condition in i, we assign (:=) the Continent to 'AUS'

library(data.table)
setDT(gsample)[MAKE=='HOLDEN', Continent:= 'AUS']

注意：我们假设'Continent'列是字符 class。

NOTE: We assumed that the 'Continent' column is character class.

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