title: Continuous value supplied to discrete scale ggplot2
body: <p>when I tried to plot a graph of decision boundary in R, I met some problem and it returned a error "Continuous value supplied to discrete scale". I think the problem happened in the scale_colur_manual but I don't know how to fix it. Below is the code attached.</p>
  
  <pre><code>library(caTools)
  set.seed(123)
  split = sample.split(df$Purchased,SplitRatio = 0.75)
  training_set = subset(df,split==TRUE)
  test_set = subset(df,split==FALSE)
  
  # Feature Scaling
  training_set[,1:2] = scale(training_set[,1:2])
  test_set[,1:2] = scale(test_set[,1:2])
  
  # Fitting logistic regression to the training set
  lr = glm(formula = Purchased ~ .,
           family = binomial,
           data = training_set)
  
   #Predicting the test set results
   prob_pred = predict(lr,type = 'response',newdata = test_set[-3])
   y_pred = ifelse(prob_pred &gt; 0.5, 1, 0)
  
   #Making the Confusion Matrix
   cm = table(test_set[,3],y_pred)
   cm
  
   #Visualizing the training set results
   library(ggplot2)
  
   set = training_set
  
   X1 = seq(min(set[, 1]) - 1, max(set[, 1]) + 1, by = 0.01)
  
   X2 = seq(min(set[, 2]) - 1, max(set[, 2]) + 1, by = 0.01)
  
   grid_set = expand.grid(X1, X2)
  
   colnames(grid_set) = c('Age', 'EstimatedSalary')
  
   prob_set = predict(lr, type = 'response', newdata = grid_set)
  
   y_grid = ifelse(prob_set &gt; 0.5, 1,0)
  
  
   ggplot(grid_set) +
  
         geom_tile(aes(x = Age, y = EstimatedSalary, fill = factor(y_grid)),
  
         show.legend = F) +
  
   geom_point(data = set, aes(x = Age, y = EstimatedSalary, color = Purchased),
  
           show.legend = F) +
  
   scale_fill_manual(values = c("orange", "springgreen3")) +
  
   scale_colour_manual(values = c("red3", "green4")) +
  
   scale_x_continuous(breaks = seq(floor(min(X1)), ceiling(max(X2)), by = 1)) +
  
   labs(title = "Logistic Regression (Training set)",
  
        ylab = "Estimated Salary", xlab = "Age")
  </code></pre>