Working with violin plot

Hi

I would like to use the violin plot as described in the manual [1]. In the example, I see

ToothGrowth$dose <- as.factor(ToothGrowth$dose)
head(ToothGrowth)

On the other hand, my data is a csv file containing some rows and numbers. Problem is that the following code doesn't work

mydata <- read.csv('test.csv', header=T,row.names=1)
mydata

V1  V2   V3 V4
P1 73.6 0.7 74.6  R
P2 75.2 0.7 75.8  R
P3  6.5 0.0  7.3  R
P4 41.4 0.3 39.2  C
P5  5.4 0.1 18.2  C
P6 18.8 0.3 30.3  C

library(ggplot2)
p <- ggplot(ToothGrowth, aes(x=V4, y=V1)) + geom_violin()
p

Error in FUN(X[[i]], ...) : object 'V4' not found


Any idea to fix that?





[1] http://www.sthda.com/english/wiki/ggplot2-violin-plot-quick-start-guide-r-software-and-data-visualization


Regards,
Mahmood