Add titles

Plot titles can be specified either directly to the plotting functions during the plot creation or by using the title() function (to add titles on an existing plot).

# Add titles
barplot(c(2,5), main="Main title",
        xlab="X axis title",
        ylab="Y axis title",
        sub="Sub-title",
        col.main="red", col.lab="blue", col.sub="black")
# Increase the size of titles
barplot(c(2,5), main="Main title",
        xlab="X axis title",
        ylab="Y axis title",
        sub="Sub-title",
        cex.main=2, cex.lab=1.7, cex.sub=1.2)

To read more, click on this link : Add titles to a plot in R software. You will learn about how to change font styles (italic, bold, bold-italic) and, to modify a graph titles using title() or par() R functions.

Add legends

The legend() function can be used. A simplified format is :

legend(x, y=NULL, legend, col)

# Generate some data
x<-1:10; y1=x*x; y2=2*y1
# First line plot
plot(x, y1, type="b", pch=19, col="red", xlab="x", ylab="y")
# Add a second line
lines(x, y2, pch=18, col="blue", type="b", lty=2)
# Add legends
legend("topleft", legend=c("Line 1", "Line 2"),
       col=c("red", "blue"), lty=1:2, cex=0.8)

Read more (change the border and the background color of the legend box; specify the position for legends using keywords, …) —> Add legends to plots

Add texts

To add a text to a plot in R, the text() function [to draw a text inside the plotting area] and mtext()[to put a text in one of the four margins of the plot] function can be used.

A simplified format for text() is :

text(x, y, labels)

plot(cars[1:10,], pch=19)
text(cars[1:10,],  row.names(cars[1:10,]), 
     cex=0.65, pos=1,col="red") 

Read more (add texts in the margins of a graph; add mathematical annotation, …) —> Add text to a plot

Add straight lines

The R function abline() can be used to add straight lines (vertical, horizontal or regression lines) to a graph.

A simplified format is :

abline(a=NULL, b=NULL, h=NULL, v=NULL, ...)

# Add horizontal and vertical lines
#++++++++++++++++++++++++++++++++++
plot(cars, pch=19)
abline(v=15, col="blue") # Add vertical line
# Add horizontal line, change line color, size and type
abline(h=60, col="red", lty=2, lwd=3)
# Fit regression line
#++++++++++++++++++++++++++++++++++
require(stats)
reg<-lm(dist ~ speed, data = cars)
coeff=coefficients(reg)
# equation of the regression line : 
eq = paste0("y = ", round(coeff[2],1), "*x ", round(coeff[1],1))
plot(cars, main=eq, pch=18)
abline(reg, col="blue", lwd=2)

Read more —> abline R function : An easy way to add straight lines to a plot using R software

Add an axis to a plot

axis() function can be used.

A simplified format is :

axis(side, at=NULL, labels=TRUE)

x<-1:4; y=x*x
plot(x, y, pch=18, col="red", type="b",
     frame=FALSE, xaxt="n") # Remove x axis
axis(1, 1:4, LETTERS[1:4], col.axis="blue")
axis(3, col = "darkgreen", lty = 2, lwd = 0.5)
axis(4, col = "violet", col.axis = "dark violet", lwd = 2)

Read more —> Add an axis to a plot with R software.

Change axis scale : minimum, maximum and log scale

xlim and ylim arguments can be used to change the limits for x and y axis. Format : xlim = c(min, max); ylim = c(min, max).

log transformation can be performed using the parameters : log=“x”, log=“y” or log=“xy”.

x<-1:10; y=x*x
plot(x, y) # Simple graph
plot(x, y, xlim=c(1,15), ylim=c(1,150))# Enlarge the scale
plot(x, y, log="y")# Log scale

Read more —> Axis scale in R software : minimum, maximum and log scale.

Change plotting symbols

The following points symbols can be used in R :

Point symbols can be changed using the argument pch.

x<-c(2.2, 3, 3.8, 4.5, 7, 8.5, 6.7, 5.5)
y<-c(4, 5.5, 4.5, 9, 11, 15.2, 13.3, 10.5)
# Change plotting symbol using pch
plot(x, y, pch = 19, col="blue")
plot(x, y, pch = 18, col="red")
plot(x, y, pch = 24, cex=2, col="blue", bg="red", lwd=2)

Read more —> R plot pch symbols : The different point shapes available in R.

Change line types

The following line types are available in R :

Line types can be changed using the graphical parameter lty.

x=1:10; y=x*x
plot(x, y, type="l") # Solid line (by default)
plot(x, y, type="l", lty="dashed")# Use dashed line type
plot(x, y, type="l", lty="dashed", lwd=3)# Change line width

Read more —> Line types in R : lty.

Change colors

Colors can be specified by names (e.g col=red) or with hexadecimal code (e.gcol = “#FFCC00”).

# use color names
barplot(c(2,5), col=c("blue", "red"))
# use hexadecimal color code
barplot(c(2,5), col=c("#009999", "#0000FF"))

Hexadecimal color charts :

(Source: http://www.visibone.com)

RColorBrewer package can also be used to create a nice looking color palettes. Read our article : Colors in R.

Read more —> Colors in R.

Related articles

Click on the following articles to read more.

Plotting symbols in R

Different plotting symbols are available in R. The graphical argument used to specify point shapes is pch.

Line types in R

The argument lty can be used to specify the line type. To change line width, the argument lwd can be used.

Colors in R

Colors can be specified either by name (e.g col = “red”) or as a hexadecimal code (such as col = “#FFCC00”). You can also use other color systems such as ones taken from the RColorBrewer package.

Add titles to a plot

Plot titles can be specified either directly to the plotting functions during the plot creation or by using the title() function (to add titles on an existing plot).

Add legends to plots

To add legends to plots in R, the R legend() function can be used.

Add texts to a plot

To add a text to a plot in R, the text() and mtext() R functions can be used.

Add straight lines

The R function abline() can be used to add vertical, horizontal or regression lines to a graph.

Add an axis to a plot

axis() function can be used to add a secondary axis to a plot.

Change axis scale in R

The goal of this article is to show you how to set x and y axis limites by specifying the minimum and the maximum values of each axis. We’ll also see how to set the log scale.

Infos

This analysis has been performed using R statistical software (ver. 3.1.0).

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