RMarkdown : Multiple ggplots in same chunk using loop

Question

我正在尝试在 RMarkdown 文档的单个 block 中使用 for 循环生成多个图(在 ggplot2 中)。

当我对代码进行硬编码以生成这两个图时，图按预期呈现。请参阅我的代码中标题为“硬编码方法”的部分。

但是，当我为列表中的两个图加载参数并循环遍历列表时，图没有显示出来。我也没有看到任何错误。请参阅我的代码中标题为“循环方法”的部分。

谁能告诉我这是怎么回事，我该如何解决？谢谢。

• 卡尔提克。

这是我的代码:

---
title: "Test for multiple plots"
author: "KC"
date: "4/3/2020"
output: html_document
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)
```

# Hardcoded Method

Sample Plot - One plot at a time 

```{r Multiple Plots separately listed, echo=TRUE, fig.keep="all"}
library(ggplot2)
library(datasets)

combo = c("temperature", "pressure")
ggplot(pressure, 
       mapping=aes(x=base::get(combo[1]), y=base::get(combo[2]))) + 
  geom_point() + 
  labs(x=combo[1], 
       y=combo[2], 
       title=paste("Hardcoded Method:", paste(combo, collapse=" vs ")))

combo = c("pressure", "temperature")
ggplot(pressure, 
       mapping=aes(x=base::get(combo[1]), y=base::get(combo[2]))) + 
  geom_point() + 
  labs(x=combo[1], 
       y=combo[2], 
       title=paste("Hardcoded Method:", paste(combo, collapse=" vs ")))

```

# Loop Method

Now, I use a loop method to generate the same plots.  

```{r Multiple Plots in a loop, echo=TRUE, fig.keep="all"}
library(ggplot2)
library(datasets)
combos = list(c("temperature", "pressure"), c("pressure", "temperature"))

for (combo in combos) {
  # combo = combos[[1]]
  print(paste("Plotting", paste(combo, collapse=" vs ")))
  ggplot(pressure, 
         mapping=aes(x=base::get(combo[1]), y=base::get(combo[2]))) + 
    geom_point() + 
    labs(x=combo[1], 
         y=combo[2], 
         title=paste("Loop Method:", paste(combo, collapse=" vs ")))
}

```

Answer 1

在包含 Markdown 文件的代码块中使用 for 循环时，您需要显式地 print() 绘图。因此，以下代码将不起作用:

for (i in length(x)) {
    ggplot(...)
}

你需要转换成这样的东西:

for (i in length(x)) {
    p <- ggplot(...)
    print(p)
}