R-DPLYR0.4.1:如何在函数中通过列名进行总结

Question

data <- data.frame(section=rep(c("A","B"),3), quantity=c(6:11))
#I need to get this result : 
RESULT = data %>% group_by(section) %>% summarise(total=sum(quantity))

# function : 
synthetize = function(x,column,measure){
  result = x %>% group_by(column) %>% summarise(total=sum(measure))
}
RESULT2=synthetize(data,column="section",measure="quantity")
RESULT2

我尝试了eval、get，但看起来这没有帮助

Answer 1

我们可以使用rlang::sym将字符串转换为符号并求值(！！)

library(tidyverse)
synthetize = function(x, column, measure){
     x %>% 
        group_by_at(column) %>%
        summarise(total=sum(!! rlang::sym(measure)))
   }

synthetize(data, column="section", measure="quantity")
# A tibble: 2 x 2
#  section total
#   <fct>   <int>
#1 A          24
#2 B          27

注意：这里我们使用了OP相同的参数类型

如果我们使用的是dplyr的旧版本，下面的内容可能会有所帮助

library(lazyeval)
synthetize2 = function(x, column, measure){

  x %>% 
     group_by_(column) %>%
     summarise(total = interp(~ sum(v1), v1 = as.name(measure)))


synthetize2(data, column='section', measure='quantity')