How to shade area between lines in ggplot2

-----Original Message-----
From: Luigi Marongiu <marongiu.luigi at gmail.com>
Sent: Friday, October 23, 2020 11:11 AM
To: PIKAL Petr <petr.pikal at precheza.cz>
Cc: r-help <r-help at r-project.org>
Subject: Re: [R] How to shade area between lines in ggplot2

also from this site: https://plotly.com/ggplot2/geom_ribbon/
I get the answer is geom_ribbon but I am still missing something ``` #! plot 
p
= ggplot(data = trainset, aes(x=x, y=y, color=z)) +
  geom_point() + scale_color_manual(values = c("red", "blue")) # show
support vectors df_sv = trainset[svm_model$index, ] p = p +
geom_point(data = df_sv, aes(x=x, y=y),
                   color="purple", size=4, alpha=0.5) # show hyperplane 
(decision
boundaries are off set by 1/w[2]) w = t(svm_model$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, col =
"royalblue4")
p = p +     geom_ribbon(aes(ymin=intercept_1 - 1/w[2],
                            ymax=intercept_1 + 1/w[2],
                            x=x, fill = "band"), alpha = 0.3) +
  scale_fill_manual("",values="grey12")
```

On Fri, Oct 23, 2020 at 10:26 AM PIKAL Petr <petr.pikal at precheza.cz> wrote:

Hi

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

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

Cheers
Petr

-----Original Message-----
From: R-help <r-help-bounces at r-project.org> On Behalf Of Luigi
Marongiu
Sent: Friday, October 23, 2020 9:59 AM
To: r-help <r-help at 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

--
Best regards,
Luigi