[R] How to shade area between lines in ggplot2

[Rui Barradas]

Hello,

What about this?


straightline <- function(x, slope, intercept) slope*x + intercept

p <- ggplot(data = trainset, aes(x=x, y=y, color=z)) +
   geom_point() +
   geom_ribbon(aes(ymin = straightline(x, slope_1, intercept_1 + 1/w[2]),
                   ymax = straightline(x, slope_1, intercept_1 - 1/w[2])),
               color = NA, fill = "grey", alpha = 0.5) +
   geom_abline(slope = slope_1, intercept = intercept_1) +
   scale_color_manual(values = c("red", "blue"))

p


Note that now the middle line is drawn last. Otherwise it will be greyed 
by the ribbon.

Hope this helps,

Rui Barradas

Às 08:58 de 23/10/20, Luigi Marongiu escreveu:
> Hello,
> I am running SVM and showing the results with ggplot2. The results
> include the decision boundaries, which are two dashed lines parallel
> to a solid line. I would like to remove the dashed lines and use a
> shaded area instead. How can I do that?
> Here is the code I wrote..
> ```
> library(e1071)
> library(ggplot2)
> 
> set.seed(100)
> x1 = rnorm(100, mean = 0.2, sd = 0.1)
> y1 = rnorm(100, mean = 0.7, sd = 0.1)
> y2 = rnorm(100, mean = 0.2, sd = 0.1)
> x2 = rnorm(100, mean = 0.75, sd = 0.1)
> df = data.frame(x = c(x1,x2), y=c(y1,y2),
>                  z=c(rep(0, length(x1)), rep(1, length(x2))))
> df$z = factor(c(rep(0, length(x1)), rep(1, length(x2))))
> df[, "train"] <- ifelse(runif(nrow(df)) < 0.8, 1, 0)
> trainset <- df[df$train == 1, ]
> testset <- df[df$train == 0, ]
> trainColNum <- grep("train", names(df))
> trainset <- trainset[, -trainColNum]
> testset <- testset[, -trainColNum]
> head(trainset); str(df)
> 
> svm_model<- svm(z ~ .,
>                  data = trainset,
>                  type = "C-classification",
>                  kernel = "linear",
>                  scale = FALSE)
> 
> #! plot
> p = ggplot(data = trainset, aes(x=x, y=y, color=z)) +
>    geom_point() + scale_color_manual(values = c("red", "blue"))
> # show decision boundaries
> w = t(svm_model$coefs) %*% svm_model$SV  # %*% = matrix multiplication
> slope_1 = -w[1]/w[2]
> intercept_1 = svm_model$rho / w[2]
> p = p + geom_abline(slope = slope_1, intercept = intercept_1)
> ### here we go: can I use a shaded area between these two lines? ###
> p = p + geom_abline(slope = slope_1, intercept = intercept_1 - 1/w[2],
>                      linetype = "dashed") +
>    geom_abline(slope = slope_1, intercept = intercept_1 + 1/w[2],
>                linetype = "dashed")
> print(p)
> 
> ```
> 
> Thank you
>