[R] Adding non-data line to legend ggplot2 Maximum Contaminant Level

[John Kane]

Well, here is one way but it seems a bit clumsy.
In words, I created a new data.frame with "250" in the Chloride vector and "SMCL" in the Detections vector and supplessed one legend. 
Warning: For my convenience I am using different data.frame names . 

library(ggplot2)

MyData <-read.csv("http://doylesdartden.com/Stats/TimeSeriesExample.csv", sep=",")

MyData$Detections <- ifelse(MyData$D_Chloride ==1, "Detected", "NonDetect")


dat1 <-  MyData[, c(1, 3, 4, 6)]

dat2 <-  dat1[, c(1,2)]

dat2$Detections <-  rep("SMCL", nrow(dat2))
dat$Chloride <-  rep(250, nrow(dat2))

dat3 <-  rbind(dat1, dat2)

p <-  ggplot(dat3, aes(Year, Chloride, colour = Detections)) + 
           geom_point(aes(shape=Detections), show.legend = F) +
           geom_line( aes(Year, Chloride))

    On Tuesday, October 3, 2017, 3:17:00 PM EDT, David Doyle <kydaviddoyle at gmail.com> wrote:  
 
 Hi John,
I used your recommendation of adding a new variable (see below) and it is plotting the line at the 250 mg/L mark but I still can not figure out how to get it added to the legend.
Thanks again for your help.
David


#Loads the ggplot2 package.  NOTE you have to install it before hand.library(ggplot2)
##This loads your data from your worksheetMyData <-read.csv("http://doylesdartden.com/Stats/TimeSeriesExample.csv", sep=",")

#Sets which are detections and nondetects
MyData$Detections <- ifelse(MyData$D_Chloride ==1, "Detected", "NonDetect")
# adds my screening LevelMyData$SMCL <- rep(250, nrow(MyData))
#does the plotp <- ggplot(data = MyData, aes(x=Year, y=Chloride, col=Detections)) +  geom_point(aes(shape=Detections)) +  geom_line(data = MyData,aes(y=SMCL))+    #sets the detect vs. non-detect colors  scale_colour_manual(values=c("black","red")) +     #sets the y scale and log base 10  scale_y_log10() +    #location of the legend    theme(legend.position=c("right")) +    #sets the line color, type and size  geom_line(colour="black", linetype="dotted", size=0.5) + 
  ylab("Chloride (mg/L)")
## does the graph using the Location IDs as the different Locations.p + facet_grid(Location ~ .)

On Mon, Oct 2, 2017 at 5:09 AM, John Kane <jrkrideau at yahoo.ca> wrote:

MyData$newvar <- rep(250, nrow(MyData))
Again, I have not tried graphing this. 
 

    On Sunday, October 1, 2017, 10:38:09 PM EDT, David Doyle <kydaviddoyle at gmail.com> wrote:  
 
 Hi John,
How do I add a second y variable? ThanksDavid
On Sun, Oct 1, 2017 at 5:44 AM, John Kane <jrkrideau at yahoo.ca> wrote:

I just glanced at the problem but I think you would have to create a new variable to replace the hline. What about adding some text annotation in the graph instead?
 

    On Tuesday, September 26, 2017, 3:51:46 PM EDT, David Doyle <kydaviddoyle at gmail.com> wrote:  
 
 Hello everyone,

I have a plot showing chloride concentrations for various point over time.
I also have a dotted line that show the Secondary Maximum Contaminant Level
(my screening limit) on the graphs at 250 mg/L.  But I can not figure out
how to include the dotted line / Secondary Maximum Contaminant Level in
the legend.  Any thoughts?  My code is as following and is linked to my
data on the net.

Thank you in advance
David


#Loads the ggplot2 package.
library(ggplot2)

##This loads your data from your worksheet
MyData <-read.csv("http:// doylesdartden.com/Stats/ TimeSeriesExample.csv",
sep=",")


#Sets which are detections and nondetects

MyData$Detections <- ifelse(MyData$D_Chloride ==1, "Detected", "NonDetect")

#does the plot
p <- ggplot(data = MyData, aes(x=Year, y=Chloride , col=Detections)) +
  geom_point(aes(shape= Detections)) +

  #sets the detect vs. non-detect colors
  scale_colour_manual(values=c(" black","red")) +

  #sets the y scale and log base 10
  scale_y_log10() +

  ##adds line
  geom_hline(aes(yintercept=250) ,linetype="dashed")+

  #location of the legend
  theme(legend.position=c(" right")) +

  #sets the line color, type and size
  geom_line(colour="black", linetype="dotted", size=0.5) +
  ylab("Chloride (mg/L)")

## does the graph using the Location IDs as the different Locations.
p + facet_grid(Location ~ .)

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