在mutate和合并中使用变量名 [英] Using variable name in mutate and coalesce

问题描述

我有以下一段代码，它合并了两个数据帧：

I have the following piece of code that merges two dataframes:

prim <- data.frame("t"=2007:2012,
                   "a"=1:6,
                   "b"=7:12)

secnd <- data.frame("t"=2012:2013,
                    "a"=c(5, 7))

final_df <- prim %>% full_join(secnd, by = 't') %>%
  mutate(a = coalesce(as.integer(a.y),a.x)) %>%
  select(t,a,b)

是否可以使用变量名而不是hard-如上所述对 a 进行编码？即，是否可以使以下无效代码正常工作？

Is it possible to use a variable name instead of hard-coding a as done above? I.e., is it possible to make the following non-functioning code work?

var <- "a"
final_df <- prim %>% full_join(secnd, by = 't') %>%
  mutate(var = coalesce(as.integer(var.y),var.x)) %>%
  select(t,var,b)

推荐答案

一种选择是用 syms 转换为符号并求值（ !!! ）

One option would be to convert to symbol with syms and evaluate (!!!)

library(tidyverse)
var <- "a"
prim %>% 
  full_join(secnd, by = "t") %>%
  mutate_at(vars(starts_with(var)), as.integer) %>% 
  transmute(t, !! var := coalesce(!!! rlang::syms(paste0(var, c(".y", ".x")))), b)
#     t a  b
#1 2007 1  7
#2 2008 2  8
#3 2009 3  9
#4 2010 4 10
#5 2011 5 11
#6 2012 5 12
#7 2013 7 NA

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