Extract Equation of Linear Regression Line in R (Example Code)

This tutorial illustrates how to get the equation of a linear regression slope in the R programming language.

Creation of Example Data

data(iris)                           # Load example data
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

Example: Returning Equation of Linear Trend Line

mod <- lm(Sepal.Length ~ ., iris)    # Estimate regression model using lm()
summary(mod)                         # Print descriptive statistics
# Call:
# lm(formula = Sepal.Length ~ ., data = iris)
# 
# Residuals:
#      Min       1Q   Median       3Q      Max 
# -0.79424 -0.21874  0.00899  0.20255  0.73103 
# 
# Coefficients:
#                   Estimate Std. Error t value Pr(>|t|)    
# (Intercept)        2.17127    0.27979   7.760 1.43e-12 ***
# Sepal.Width        0.49589    0.08607   5.761 4.87e-08 ***
# Petal.Length       0.82924    0.06853  12.101  < 2e-16 ***
# Petal.Width       -0.31516    0.15120  -2.084  0.03889 *  
# Speciesversicolor -0.72356    0.24017  -3.013  0.00306 ** 
# Speciesvirginica  -1.02350    0.33373  -3.067  0.00258 ** 
# ---
# Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
# 
# Residual standard error: 0.3068 on 144 degrees of freedom
# Multiple R-squared:  0.8673,	Adjusted R-squared:  0.8627 
# F-statistic: 188.3 on 5 and 144 DF,  p-value: < 2.2e-16
mod_eq <- paste("Sepal.Length =",    # Specify equation of line
                round(coef(mod)[[1]], 2),
                "+",
                paste(round(as.numeric(coef(mod)[2:length(coef(mod))]), 2),
                      "*",
                      names(coef(mod)[2:length(coef(mod))]),
                      "+",
                      collapse = " "))
mod_eq <- substr(mod_eq, 1, nchar(mod_eq) - 2)
mod_eq <- gsub("\+ -", "- ", mod_eq)
mod_eq                               # Print equation of line
# [1] "Sepal.Length = 2.17 + 0.5 * Sepal.Width + 0.83 * Petal.Length - 0.32 * Petal.Width - 0.72 * Speciesversicolor - 1.02 * Speciesvirginica"

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