R Scatterplots - r - learn r - r programming
- A scatter plot pairs up values of two quantitative variables in a data set and display them as geometric points inside a Cartesian diagram.
- Scatterplots show many points plotted in the Cartesian plane. Each point represents the values of two variables.
- One variable is chosen in the horizontal axis and another in the vertical axis.
- The simple scatterplot is created using the plot() function.
Syntax
- The basic syntax for creating scatterplot in R is
plot(x, y, main, xlab, ylab, xlim, ylim, axes)
- Following is the description of the parameters used −
- x is the data set whose values are the horizontal coordinates.
- y is the data set whose values are the vertical coordinates.
- main is the tile of the graph.
- xlab is the label in the horizontal axis.
- ylab is the label in the vertical axis.
- xlim is the limits of the values of x used for plotting.
- ylim is the limits of the values of y used for plotting.
- axes indicates whether both axes should be drawn on the plot.
Example
- We use the data set "mtcars" available in the R environment to create a basic scatterplot. Let's use the columns "wt" and "mpg" in mtcars.
Sample Code
input <- mtcars[,c('wt','mpg')]
print(head(input))
Output
wt mpg
Mazda RX4 2.620 21.0
Mazda RX4 Wag 2.875 21.0
Datsun 710 2.320 22.8
Hornet 4 Drive 3.215 21.4
Hornet Sportabout 3.440 18.7
Valiant 3.460 18.1
Creating the Scatterplot
- The below script will create a scatterplot graph for the relation between wt(weight) and mpg(miles per gallon).
Sample Code
# Get the input values.
input <- mtcars[,c('wt','mpg')]
# Give the chart file a name.
png(file = "scatterplot.png")
# Plot the chart for cars with weight between 2.5 to 5 and mileage between 15 and 30.
plot(x = input$wt,y = input$mpg,
xlab = "Weight",
ylab = "Milage",
xlim = c(2.5,5),
ylim = c(15,30),
main = "Weight vs Milage"
)
# Save the file.
dev.off()Output
- When we execute the above code, it produces the following result
Scatterplot Matrices
- When we have more than two variables and we want to find the correlation between one variable versus the remaining ones we use scatterplot matrix.
- We use pairs() function to create matrices of scatterplots.
Syntax
- The basic syntax for creating scatterplot matrices in R is
pairs(formula, data)
- Following is the description of the parameters used −
- formula represents the series of variables used in pairs.
- data represents the data set from which the variables will be taken.
Sample Code
- Each variable is paired up with each of the remaining variable. A scatterplot is plotted for each pair.
# Give the chart file a name.
png(file = "scatterplot_matrices.png")
# Plot the matrices between 4 variables giving 12 plots.
# One variable with 3 others and total 4 variables.
pairs(~wt+mpg+disp+cyl,data = mtcars,
main = "Scatterplot Matrix")
# Save the file.
dev.off()
Output
- When the above code is executed we get the following output.
