在R中传递值 [英] Pass by value in R

问题描述

当试图调用grid.arrange在同一个ggplot2图上放置多个图时，我首先创建了我想要的图的列表。然后我构建相应的参数列表来调用grid.arrange，正如解释在前一个问题中。这是我的代码（我的数据框叫做manip）：

  args.list<  -  NULL; 
 plot.list<  -  NULL; 
 for（m in names（manip [2:10]））{
 plot.list< -c（plot.list，list（qplot（manip $ side，y = manip [，m] ，ylab = m））
} 
 args.list<  -  c（plot.list，1,9）
 names（args.list）<  -  c（names（manip） [2:10]，list（nrow，ncol））
 do.call（grid.arrange，args.list）
  

除了9个图完全相同之外，它可以工作！检查后，数据总是与 m = 10 。所以我猜测 m 的值不是在循环中赋值的，而是稍后评估的，但是标签 ylab = m 是正确分配的，并且对于所有图形都是不同的。

有什么区别，以及解释者如何选择何时评估m的情节。有人可以解释吗？ 解决方案

我会先回答您的问题，然后显示一个替代使用方面的阴谋。

编辑

下面的代码看起来很简单：

 <$ c $ （2），
 function（x）qplot（manip $ mpg，y = manip [， x 
 
 $ name $（$）
 do.call（grid.arrange，c（plot.list，nrow = 10））
   
 
 
 
 
 
 
我知道。但是，你是否考虑过使用facet代替你的情节？
 
 
 
以下代码更为简单：执行查询并生成易于解释的图形：
 
 
 $ p $ lt; code> library（reshape2）
 manip<  -  mtcars 
 mmanip<  -  melt（manip，id.vars = mpg）
 str（mmanip）
 ggplot（mmanip，aes（x = mpg，y = value））+ 
 geom_point（stat =identity）+ 
 facet_grid（ 。〜variable，scales =free）
  

When trying to call grid.arrange to put multiple plots on a same ggplot2 graph, I first build a list of the plots I want. Then I build the corresponding argument list to call grid.arrange, as was explained in a previous question. This is my code (my dataframe is called manip):

args.list <- NULL;
plot.list <- NULL;
for (m in names(manip[2:10])) {
  plot.list <- c(plot.list, list(qplot(manip$side, y=manip[,m],ylab=m))
}
args.list <- c(plot.list, 1, 9)
names(args.list) <- c(names(manip)[2:10], list("nrow","ncol"))
do.call(grid.arrange, args.list)

This works, except that the 9 graphs are exactly the same! After checking, it turns out that the data is always the one corresponding to m=10. So my guess was that the value of m is not assigned in the loop, but evaluated later. However, the label ylab=m is assigned correctly and is different for all the graphs.

So I don't really get what the difference is and how the interpreter chooses when to evaluate m for the plots. Can someone explain?

解决方案

I will first answer your question and then show an alternative using a facet plot.

Edited

The following, much simplified, code seems to work:

library(gridExtra)
manip <- mtcars
plot.list <- lapply(2:11, 
                    function(x)qplot(manip$mpg, y=manip[, x], 
                    ylab=names(manip)[x]))
do.call(grid.arrange, c(plot.list, nrow=10))

It produces this ugly plot:

---

Without knowing your objectives, it is dangerous to try and give advice, I know. Nonetheless, have you considered using facets for your plot instead?

The following code is much simpler, executes quiker and produces a graph that is easier to interpret:

library(reshape2)
manip <- mtcars
mmanip <- melt(manip, id.vars="mpg")
str(mmanip)
ggplot(mmanip, aes(x=mpg, y=value)) + 
    geom_point(stat="identity") + 
    facet_grid(.~variable, scales="free")

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