如何在R中使用vioplot绘制分类数据与数值数据？

Question

I have a data set with a categorical column "colors", which has 4 colors. One of the other 2 columns is quantitative, and is called "pollen". I am trying to get vioplot to make 4 separate violin plots color vs pollen. Here is a data sample

The data is available at http://www.uwyo.edu/crawford/datasets/beeflowers.txt

I made 4 subsets of the data with

blue <- subset(beeflowers4, colors=="blue", select=c(pollen, colors))
green <- subset(beeflowers4, colors=="green", select=c(pollen, colors))
purple <- subset(beeflowers4, colors=="pruple", select=c(pollen, colors))
red <- subset(beeflowers4, colors=="red", select=c(pollen, colors))

I then tried to plot a violin plot with

vioplot(blue, green, purple, red, names=c("blue", "green", "purple", "red"), col="yellow")

However I got this error

#Error in FUN(X[[1L]], ...) : 
#  only defined on a data frame with all numeric variables

Is there anyway for vioplot to plot pollen vs colors?

Answer 1

Here's another way that is much less repetitive. When you find yourself typing the same thing over and over, like those four lines of subsets, it's a sign that there's a more efficient way.

In this case, ggplot takes data in the long form that you already have, so there's no need for any sub-setting or reshaping.

# import data
x <- read.table("http://www.uwyo.edu/crawford/datasets/beeflowers.txt", 
                stringsAsFactors = FALSE,
                header = TRUE)

# inspect
str(x); View(x)

# get rid of that 999, presumably missing data
x <- x[x$pollen != 999, ]

# plot
library(ggplot2)
ggplot(x, aes(colors, pollen)) +
  geom_violin()

Answer 2

You misspelled "purple" when you subsetted. Also, in the vioplot function, your first four arguments need to be vectors, not data frames. This code should work.

blue <- subset(beeflowers4, colors=="blue", select=c(pollen, colors))

green <- subset(beeflowers4, colors=="green", select=c(pollen, colors))

purple <- subset(beeflowers4, colors=="purple", select=c(pollen, colors))

red <- subset(beeflowers4, colors=="red", select=c(pollen, colors))

vioplot(blue$pollen, green$pollen, purple$pollen, red$pollen, names=c("blue", "green", "purple", "red"), col="yellow")