[R] How to shade area between lines in ggplot2

[PIKAL Petr]

Hi

Did you try google? I got several answers using your question

e.g.
https://stackoverflow.com/questions/54687321/fill-area-between-lines-using-g
gplot-in-r

Cheers
Petr

> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Luigi Marongiu
> Sent: Friday, October 23, 2020 9:59 AM
> To: r-help <r-help using r-project.org>
> Subject: [R] How to shade area between lines in ggplot2
> 
> 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
> 
> --
> Best regards,
> Luigi
> 
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