Question

无论如何将字符串作为列引用传递给dplyr过程？

这是一个示例 - 使用分组数据集和一个简单函数，我尝试将字符串作为引用传递给列。谢谢！

machines <- data.frame(Date=c("1/31/2014", "1/31/2014", "2/28/2014", "2/28/2014", "3/31/2014", "3/31/2014"), 
            Model.Num=c("123", "456", "123", "456", "123", "456"), 
            Cost=c(200, 300, 250, 350, 300, 400))

my.fun <- function(data, colname){
    mutate(data, position=cumsum(as.name(colname)))
}

machines <- machines %>% group_by(Date, Model.Num)     
machines <- my.fun(machines, "Cost")

Answer 1

这是一个使用 lazyeval 程序包中interp()的选项，该程序包随 dplyr 安装一起提供。在您的函数内部，您需要使用 dplyr 函数的标准评估版本。在这种情况下，这将是mutate_()。

请注意，由于您在position中设置分组的方式，新列Cost将与machines列相同。对my_fun()的第二次调用表明它正在处理一组不同的分组变量。

library(dplyr)
library(lazyeval)

my_fun <- function(data, col) {
    mutate_(data, position = interp(~ cumsum(x), x = as.name(col)))
}

my_fun(machines, "Cost")
#        Date Model.Num Cost position
# 1 1/31/2014       123  200      200
# 2 1/31/2014       456  300      300
# 3 2/28/2014       123  250      250
# 4 2/28/2014       456  350      350
# 5 3/31/2014       123  300      300
# 6 3/31/2014       456  400      400

## second example - different grouping
my_fun(group_by(machines, Model.Num), "Cost")
#        Date Model.Num Cost position
# 1 1/31/2014       123  200      200
# 2 1/31/2014       456  300      300
# 3 2/28/2014       123  250      450
# 4 2/28/2014       456  350      650
# 5 3/31/2014       123  300      750
# 6 3/31/2014       456  400     1050

Answer 2

我们可以在不使用lazyeval包的标准评估中进行评估。我们可以使用setNames将一些字符串设置为变量名。

library(tidyverse)

machines <- data.frame(
  Date = c("1/31/2014", "1/31/2014", "2/28/2014", "2/28/2014", "3/31/2014", "3/31/2014"), 
  Model.Num = c("123", "456", "123", "456", "123", "456"), 
  Cost = c(200, 300, 250, 350, 300, 400)
  )

my_fun <- function(data, col) {
  mutate_(data, .dots = setNames(paste0("cumsum(", col, ")"), "position"))
}

my_fun(machines %>% group_by(Date, Model.Num), "Cost")
# Source: local data frame [6 x 4]
# Groups: Date, Model.Num [6]
# 
# Date Model.Num  Cost position
# <fctr>    <fctr> <dbl>    <dbl>
# 1 1/31/2014       123   200      200
# 2 1/31/2014       456   300      300
# 3 2/28/2014       123   250      250
# 4 2/28/2014       456   350      350
# 5 3/31/2014       123   300      300
# 6 3/31/2014       456   400      400
my_fun(machines %>% group_by(Model.Num), "Cost")
# Source: local data frame [6 x 4]
# Groups: Model.Num [2]
# 
# Date Model.Num  Cost position
# <fctr>    <fctr> <dbl>    <dbl>
# 1 1/31/2014       123   200      200
# 2 1/31/2014       456   300      300
# 3 2/28/2014       123   250      450
# 4 2/28/2014       456   350      650
# 5 3/31/2014       123   300      750
# 6 3/31/2014       456   400     1050

dplyr字符串作为列引用

2 个答案: