英文:
How to divide only a certain factor in a column in R data frame?
问题
这是示例数据集：
library(data.table)df = data.table(x = c(1000,2000,10,2), y = c('A','A','B','B'))
我只想将 df$y == "A" 除以 1000。最终数据集应如下所示：
df = data.table(x = c(1,2,10,2), y = c('A','A','B','B'))
英文:
This is the sample dataset:
library(data.table)df = data.table(x = c(1000,2000,10,2), y = c('A','A','B','B'))
I only want to divide df$y == "A" by 1000. The final dataset should appear as:
df = data.table(x = c(1,2,10,2), y = c('A','A','B','B'))
答案1
得分: 3
在基本的R中：
df$x <- ifelse(df$y == "A", df$x/1000, df$x)
在dplyr中：
library(dplyr)df <- df %>%mutate(x = if_else(y == "A", x/1000, x))
英文:
You need to create a conditional statement.
In base R:
df$x <- ifelse(df$y == "A", df$x/1000, df$x)
In dplyr:
library(dplyr)df <- df |>mutate(x = if_else(y == "A", x/1000, x))
答案2
得分: 2
使用 `data.table` 选项，像这样使用 `fifelse`：``` rlibrary(data.table)df = data.table(x = c(1000,2000,10,2), y = c('A','A','B','B'))df[,x:=fifelse(y == "A", x/1000, x),]df#> x y#> 1: 1 A#> 2: 2 A#> 3: 10 B#> 4: 2 B
2023-02-18 创建，使用 reprex v2.0.2
<details><summary>英文:</summary>`data.table` option using `fifelse` like this:``` rlibrary(data.table)df = data.table(x = c(1000,2000,10,2), y = c('A','A','B','B'))df[,x:=fifelse(y == "A", x/1000, x),]df#> x y#> 1: 1 A#> 2: 2 A#> 3: 10 B#> 4: 2 B
<sup>Created on 2023-02-18 with reprex v2.0.2</sup>
答案3
得分: 2
我们可以使用 `data.table` 的方法，因为输入是一个 `data.table`。
library(data.table)
df[y == 'A', x := x/1000]
-输出
> df
x y
1: 1 A
2: 2 A
3: 10 B
4: 2 B
<details><summary>英文:</summary>We could use `data.table` methods as the input is a `data.table`
library(data.table)
df[y == 'A', x := x/1000]
-output
> df
x y
1: 1 A
2: 2 A
3: 10 B
4: 2 B
</details># 答案4**得分**: 1
基础R：使用[进行子集提取：
df$x[df$y == "A"] <- df$x[df$y == "A"]/1000
x y1: 1 A2: 2 A3: 10 B4: 2 B
英文:
Base R: Subsetting with [:
df$x[df$y == "A"] <- df$x[df$y == "A"]/1000
x y1: 1 A2: 2 A3: 10 B4: 2 B
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