使用RStudio中的R Markdown在函数中生成的打印图

Question

I am trying to use the R-Markdown feature in R Studio where I was trying to print plots which are generated inside a function. This is a basic run down example of what I am trying to do.

**Test printing plots generated in a function**
================================================

``` {r  fig.width=8, fig.height=4, warning=FALSE, eval=TRUE, message=FALSE, tidy=TRUE, dev='png', echo=FALSE, fig.show='hold', fig.align='center'}
dat <- data.frame(x=c(1:10),y=c(11:20),z=c(21:30),name=rep(c("a","b"),each=5))
library(ggplot2)

ex <- function(data){

  plot(data[,1],data[,2])
  plot(data[,1],data[,3])
}

for (i in 1:10){
t1 <- rbind(i,ex(dat))
}
t1
```

Those testing this code, please make sure to save it as ".Rmd" file and then run the knithtml() in RStudio toolbar. This code above works absolutely fine with the kind of html output I desire. However when I replace the base plotting function by ggplot based code, I cannot get the knithtml() to produce the ggplot output of the 10 plots that I got like before. The base plot code above is now replaced by the following code

  p1 <- ggplot(data=data, aes(x=data[,1],y=data[,2]))
  p1 <- p1+geom_point()
  p1 

Am I missing something very simple here.

VJ

Answer 1

There are two problems in your code:

1. ggplot doesn't recognize the data x and y data, bacause it works inside the data environment. You should give it the column names directly.
2. The code in yur loop doesn't make sense. You can't mix a plot with an index... (the reason it works with the base plot is through a side-effect) I've replaced it with the simple plot command.

The following will work:

**Test printing plots generated in a function**
================================================

``` {r  fig.width=8, fig.height=4, warning=FALSE, eval=TRUE, message=FALSE, tidy=TRUE, dev='png', echo=FALSE, fig.show='hold', fig.align='center'}
dat <- data.frame(x=c(1:10),y=c(11:20),z=c(21:30),name=rep(c("a","b"),each=5))
library(ggplot2)

ex <- function(data){
  p1 <- ggplot(data=data, aes(x=x,y=y))
  p1 <- p1+geom_point()
  return(p1) 
}

for (i in 1:2){
plot(ex(dat))
}

```