How to add stats. to volcano plot?

Question

[ahmad mousavi]

Hi

How can I add statistics to volcano plot in R for gene expression? Statistics like up and down number of genes and highly up and down genes.

use example code for that :

library(ggplot2)
fold_changes <- c(rnorm(20000, 0, 2))
pvalues <- runif(n=20000, min=1e-50, max=.1)
dif <- data.frame(fc =fold_changes,pv =pvalues)
dif$thershold <- ifelse(dif$fc > 1 & dif$pv < 0.01, "red", 
                        ifelse(dif$fc < -1 & dif$pv < 0.01, -1, "blue"))
ggplot(data=dif, aes(x=fc, y=-log10(pv))) +
  geom_point( size=1 ,aes(color=as.factor(thershold))) +
  theme(legend.position = "none") +
  xlim(c(-10, 10)) + ylim(c(0, 15)) +
  xlab("log2 fold change") + ylab("-log10 p-value")  + theme_bw()+
  theme(panel.grid.major = element_blank(), 
        panel.grid.minor = element_blank(),)

Like below image:

Answer 1

[cpad0112]

try annotate:

ggplot(data=dif, aes(x=fc, y=-log10(pv))) +
    geom_point( size=1 ,aes(color=as.factor(thershold))) +
    xlim(c(-10, 10)) + ylim(c(0, 6)) +
    xlab("log2 fold change") + 
    ylab("-log10 p-value")  + 
    annotate("label", x =c(-8,5), y = 4.75, label = c("400","120"), col=c("red","steelblue"))+
    annotate("text", x =c(-8,5), y = 5, label = c("50 FC>4","8FC <-4"))+
    theme_bw()+
    theme(panel.grid.major = element_blank(), 
          panel.grid.minor = element_blank(),
          legend.position = "none")

By editing x and y coordinates, you can move the text around graph, in x and y directions.

[zx8754]

Going one step further, we could calculate the x-y positions for label and text, instead of hard coding them.

[ahmad mousavi]

Hi

How can we choose proper x-y coordination in code like my example image?

Thanks

[ahmad mousavi]

thank you so much. It is helpful.

[cpad0112]

No problem. You have posted input data, code and output expected. This helps in understanding the issue better and resolve it faster. ahmad.moousavi