Welcome back

to “Computing for Molecular Biology 1”

Plan for Today

  • Graphics
    • Adding elements
    • Two variables
    • Formulas
  • Linear Regression
  • R programs

Telling Stories

Data Visualization


each individual has a position in the x axis

Ploting Factors



par(mfrow = c(1,2))
hist(birth$head, col="grey", nclass = 30)

Chosing the color

par(mfrow = c(1,2))
plot(birth$head, col="red")

Chosing the size of the symbol

par(mfrow = c(1,2))
plot(birth$head, cex=2)
plot(birth$head, cex=0.5)

Chosing the symbol

par(mfrow = c(1,2))
plot(birth$head, pch=16)
plot(birth$head, pch=".")

Chosing the type of plot

par(mfrow = c(1,2))
plot(birth$head, type = "l")
plot(birth$head, type = "o")


par(mfrow = c(1,2))
plot(birth$head, type = "l", xlim=c(1,100))
plot(birth$head, type = "o", xlim=c(1,100))

Full annotation

plot(birth$weight, main = "Weight at Birth", sub = "694 samples", ylab="weight [gr]")

Two plots in parallel

points(birth$age, pch=2)

The first one defines the scale

Two lines in parallel

plot(birth$head, type="l", ylim = c(22,55))
lines(birth$age, col="red")

Boys and Girls

plot(birth$weight[birth$sex=="M"], ylim=range(birth$weight), ylab = "weight [gr]")
points(birth$weight[birth$sex=="F"], col="blue")

Using auxiliary variables

boys <- birth$weight[birth$sex=="M"]
girls <- birth$weight[birth$sex=="F"]
plot(boys, ylim=range(birth$weight), ylab = "weight [gr]")
points(girls, col="blue")
abline(h=median(girls), col="blue")
legend("topright", c("boys","girls"), fill=c("black","blue"))


This command adds a straigth line in a specific position

  • abline(h=1) adds a horizontal line in 1
  • abline(v=2) adds a vertical line in 2
  • abline(a=3, b=4) adds an \(a +b\cdot x\) line

Scatter plots

Comparing two variables

plot(birth$age, birth$apgar5)

Add jitter to see more

plot(jitter(birth$age), jitter(birth$apgar5))

Less precise but more informative