R Error in Contrasts: Applied Only to Factors with More Levels (2 Examples)

In this R programming tutorial you’ll learn how to deal with the error “contrasts can be applied only to factors with 2 or more levels”.

Creation of Example Data

```my_df <- data.frame(col1 = c(7, 2, 5, 3, 3, 1, 5), # Creating data frame in R col2 = c(6, 1, 3, 5, 5, 1, 2), col3 = as.factor(c("A", "A", "B", "B", "A", "C", "A")), col4 = as.factor(5), outcome = c(1, 6, 9, 1, 1, 2, 7)) my_df # Showing example data in RStudio # col1 col2 col3 col4 outcome # 1 7 6 A 5 1 # 2 2 1 A 5 6 # 3 5 3 B 5 9 # 4 3 5 B 5 1 # 5 3 5 A 5 1 # 6 1 1 C 5 2 # 7 5 2 A 5 7```

Example 1: Replicating the Error Message: contrasts can be applied only to factors with 2 or more levels

```lm(outcome ~ col1 + col2 + col3 + col4, # Error when applying lm() function my_df) # Error in `contrasts<-`(`*tmp*`, value = contr.funs[1 + isOF[nn]]) : # contrasts can be applied only to factors with 2 or more levels```

Example 2: Solving the Error Message: contrasts can be applied only to factors with 2 or more levels

```lm(outcome ~ col1 + col2 + col3, # Removing col4 (only one value) from model my_df) # Call: # lm(formula = outcome ~ col1 + col2 + col3, data = my_df) # # Coefficients: # (Intercept) col1 col2 col3B col3C # 6.5019 0.9351 -1.9218 2.4447 -3.5153```