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Draw Regression Line on Plot in R

Scatter Plots - R Base Graphs

  • Pleleminary tasks
  • R base scatter plot: plot()
  • Enhanced scatter plots: car::scatterplot()
  • 3D scatter plots
  • Summary
  • Related articles
  • See also
  • Infos

Previously, we described the essentials of R programming and provided quick start guides for importing data into R.

Here, we'll describe how to make a scatter plot. A scatter plot can be created using the function plot(x, y). The function lm() will be used to fit linear models between y and x. A regression line will be added on the plot using the function abline(), which takes the output of lm() as an argument. You can also add a smoothing line using the function loess().

R base scatter plot: plot()

                x <- mtcars$wt y <- mtcars$mpg # Plot with main and axis titles # Change point shape (pch = 19) and remove frame. plot(x, y, main = "Main title",      xlab = "X axis title", ylab = "Y axis title",      pch = 19, frame = FALSE) # Add regression line plot(x, y, main = "Main title",      xlab = "X axis title", ylab = "Y axis title",      pch = 19, frame = FALSE) abline(lm(y ~ x, data = mtcars), col = "blue")              

                # Add loess fit plot(x, y, main = "Main title",      xlab = "X axis title", ylab = "Y axis title",      pch = 19, frame = FALSE) lines(lowess(x, y), col = "blue")

Enhanced scatter plots: car::scatterplot()

The function scatterplot() [in car package] makes enhanced scatter plots, with box plots in the margins, a non-parametric regression smooth, smoothed conditional spread, outlier identification, and a regression line, …

  • Install car package:
                install.packages("car")
  • Use scatterplot() function:
                library("car") scatterplot(wt ~ mpg, data = mtcars)

The plot contains:


  • the points
  • the regression line (in green)
  • the smoothed conditional spread (in red dashed line)
  • the non-parametric regression smooth (solid line, red)
                # Suppress the smoother and frame scatterplot(wt ~ mpg, data = mtcars,              smoother = FALSE, grid = FALSE, frame = FALSE)              

                # Scatter plot by groups ("cyl") scatterplot(wt ~ mpg | cyl, data = mtcars,              smoother = FALSE, grid = FALSE, frame = FALSE)

It's also possible to add labels using the following arguments:


  • labels: a vector of point labels
  • id.n, id.cex, id.col: Arguments for labeling points specifying the number, the size and the color of points to be labelled.
                # Add labels scatterplot(wt ~ mpg, data = mtcars,             smoother = FALSE, grid = FALSE, frame = FALSE,             labels = rownames(mtcars), id.n = nrow(mtcars),             id.cex = 0.7, id.col = "steelblue",             ellipse = TRUE)              

                ##           Mazda RX4       Mazda RX4 Wag          Datsun 710      Hornet 4 Drive   Hornet Sportabout             Valiant  ##                   1                   2                   3                   4                   5                   6  ##          Duster 360           Merc 240D            Merc 230            Merc 280           Merc 280C          Merc 450SE  ##                   7                   8                   9                  10                  11                  12  ##          Merc 450SL         Merc 450SLC  Cadillac Fleetwood Lincoln Continental   Chrysler Imperial            Fiat 128  ##                  13                  14                  15                  16                  17                  18  ##         Honda Civic      Toyota Corolla       Toyota Corona    Dodge Challenger         AMC Javelin          Camaro Z28  ##                  19                  20                  21                  22                  23                  24  ##    Pontiac Firebird           Fiat X1-9       Porsche 914-2        Lotus Europa      Ford Pantera L        Ferrari Dino  ##                  25                  26                  27                  28                  29                  30  ##       Maserati Bora          Volvo 142E  ##                  31                  32

Other arguments can be used such as:


  • log to produce log axes. Allowed values are log = "x", log = "y" or log = "xy"
  • boxplots: Allowed values are:
    • "x": a box plot for x is drawn below the plot
    • "y": a box plot for y is drawn to the left of the plot
    • "xy": both box plots are drawn
    • "" or FALSE to suppress both box plots.
  • ellipse: if TRUE data-concentration ellipses are plotted.

3D scatter plots

To plot a 3D scatterplot the function scatterplot3D [in scatterplot3D package can be used].

The following R code plots a 3D scatter plot using iris data set.

                head(iris)              
                ##   Sepal.Length Sepal.Width Petal.Length Petal.Width Species ## 1          5.1         3.5          1.4         0.2  setosa ## 2          4.9         3.0          1.4         0.2  setosa ## 3          4.7         3.2          1.3         0.2  setosa ## 4          4.6         3.1          1.5         0.2  setosa ## 5          5.0         3.6          1.4         0.2  setosa ## 6          5.4         3.9          1.7         0.4  setosa              
                # Prepare the data set x <- iris$Sepal.Length y <- iris$Sepal.Width z <- iris$Petal.Length grps <- as.factor(iris$Species) # Plot library(scatterplot3d) scatterplot3d(x, y, z, pch = 16)              

                # Change color by groups # add grids and remove the box around the plot # Change axis labels: xlab, ylab and zlab colors <- c("#999999", "#E69F00", "#56B4E9") scatterplot3d(x, y, z, pch = 16, color = colors[grps],               grid = TRUE, box = FALSE, xlab = "Sepal length",                ylab = "Sepal width", zlab = "Petal length")

  • Read more about static and interactive 3D scatter plot:
    • R base scatterplot3D
    • Amazing interactive 3D scatter plots
    • Impressive package for 3D and 4D graph
    • A complete guide to interactive 3D visualization device system in R

Summary

Create a scatter plot:

  • Using R base function:
                with(mtcars, plot(wt, mpg, frame = FALSE))
  • Using car package:
                car::scatterplot(wt ~ mpg, data = mtcars,                   smoother = FALSE, grid = FALSE)
  • 3D scatter plot:
                library(scatterplot3d) with(iris,      scatterplot3d(x = Sepal.Length, y = Sepal.Width,                     z = Petal.Length, pch = 16,                    grid = TRUE, box = FALSE) )

Infos

This analysis has been performed using R statistical software (ver. 3.2.4).


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Draw Regression Line on Plot in R

Source: http://www.sthda.com/english/wiki/scatter-plots-r-base-graphs#:~:text=A%20regression%20line%20will%20be,using%20the%20function%20loess().