dd<-matrix(0,10000,4)
for (i in 2:5){
  dd[,i-1]<-rgamma(10000,i,3)
}

dd<-as.data.frame(dd)
library(ggplot2)
library(tidyverse)
library(magrittr)
ggplot(dd%>%gather(key=shape,value=values),aes(x=values))+geom_density(aes(col=shape),alpha=0.5)
ggplot(dd%>%gather(key=shape,value=values),aes(x=values))+geom_density(aes(fill=shape),alpha=0.5)