R语言循环绘图时abline(h=0)无法添加水平线问题

你的链式调用逻辑写错了。base R的plot()是高级绘图函数，靠副作用输出图像，返回值既不是当前绘图环境，也不是传入的绘图数据。你用%>%把plot()的返回值传给with()，本质是在plot()返回的无意义对象上下文里执行abline()，根本不会作用到已经渲染好的图像上，自然加不上y=0的水平参考线。

base绘图不要硬套管道，把绘图和加参考线的步骤拆开写就行，逻辑清晰也不容易出错：

library(glue)
library(magrittr)
par(mfrow=n2mfrow(4, 2))
for(i in 1:4){
  # 先绘制散点图
  plot(savings[, i], savings[,1], xlab = glue('predictor: {i}'), ylab = 'Dependent variable')
  # 直接在当前激活的绘图设备上添加参考线，可自定义颜色、线宽方便识别
  abline(h=0, col = "red", lwd = 2)
}

如果一定要用管道写法，必须用magrittr提供的T形管道%T>%——这个管道会先执行右侧的副作用操作，再保留左侧原始输入传递下去，同时要显式触发绘图打印，不过这种写法可读性差，不推荐：

for(i in 1:4){
  plot(savings[, i], savings[,1], xlab = glue('predictor: {i}'), ylab = 'Dependent variable') %T>%
    print() %>%
    with(abline(h=0))
}

savings <- structure(list(sr = c(11.43, 12.07, 13.17, 5.75, 12.88, 8.79, 
0.6, 11.9, 4.98, 10.78, 16.85, 3.59, 11.24, 12.64, 12.55), pop15 = c(29.35, 
23.32, 23.8, 41.89, 42.19, 31.72, 39.74, 44.75, 46.64, 47.64, 
24.42, 46.31, 27.84, 25.06, 23.31), pop75 = c(2.87, 4.41, 4.43, 
1.67, 0.83, 2.85, 1.34, 0.67, 1.06, 1.14, 3.93, 1.19, 2.37, 4.7, 
3.35), dpi = c(2329.68, 1507.99, 2108.47, 189.13, 728.47, 2982.88, 
662.86, 289.52, 276.65, 471.24, 2496.53, 287.77, 1681.25, 2213.82, 
2457.12), ddpi = c(2.87, 3.93, 3.82, 0.22, 4.56, 2.43, 2.67, 
6.51, 3.08, 2.8, 3.99, 2.19, 4.32, 4.52, 3.44)), row.names = c("Australia", 
"Austria", "Belgium", "Bolivia", "Brazil", "Canada", "Chile", 
"China", "Colombia", "Costa Rica", "Denmark", "Ecuador", "Finland", 
"France", "Germany"), class = "data.frame")

内容的提问来源于stack exchange，提问作者Emil11