Custom function causing an error with returning a ggplot object and Error in eval(expr, envir, enclos) : object 'MinVal' not found

Question

I'm trying to create a custom function to return a chart object. This function seems to be having an error with calculating min/max/etc in the ggplot object.

If I run the code for the ggplot not inside a custom function it works.

To reproduce this error after I need to clear the memory with (rm(list = ls())) and reload the function and data.

How can I change my function to work correctly?

Sample data:

Date<-seq(as.Date("2000/1/1"), by = "week", length.out = 53*4)
ThousandBarrelsADay<-sample(1:1000, 53*4, replace=F)
yAxisTitle<-"Thousand Barrels per Day"
titleChart<-"test"

Function call:

p<-LinePlotTestStatsLine(Date, ThousandBarrelsADay, titleChart, yAxisTitle)

Error:

p

Error in eval(expr, envir, enclos) : object 'MinVal' not found

The code for the function:

LinePlotTestStatsLine<- function(xDateValues, yValues, titleChart, yAxisTitle) {

dfTemp=0
#the sub title outlining the data range
subtitleChart = paste("(Data set from ", min(xDateValues), " to ", max(xDateValues), ")", sep="")

#create a base dataframe
Week<- as.numeric(str_sub(ISOweek(xDateValues),start=-2))
dfTemp<-data.frame(xDateValues, Week, yValues)
dfTemp<- dfTemp[order(dfTemp$xDateValues),] 





#Summary Stat by week
dfTemp_Out<-describeBy(dfTemp$yValues, dfTemp$Week, mat = TRUE)
colnames(dfTemp_Out)[2]<-"Week"

#get the last year's of data Use 53 weeks because some years have 53 weeks
tempLast53<- tail(dfTemp, 53-length(dfTemp$yValues))
LableDateMinMax<-tempLast53$xDateValues[13]
LableDateMedian<-tempLast53$xDateValues[20]


#Chrate a base table for charting
ChartData1<-join(dfTemp_Out, tempLast53, type="inner")
#make sure the chart table is sorted
ChartData1<- ChartData1[order(ChartData1$xDateValues),] 


#find the max Date
MaxDate<- max(dfTemp$xDateValues)
maxYR<- max(year(dfTemp$xDateValues))

#min, Median, mean & max for hoizontal lines
MinVal<-min(dfTemp$yValues)
rMin<-max(which(dfTemp$yValues== MinVal, arr.ind = TRUE))
MinD<- dfTemp$xDateValues[rMin]

MaxVal<-max(dfTemp$yValues)
rMax<-max(which(dfTemp$yValues== MaxVal, arr.ind = TRUE))
MaxD<- dfTemp$xDateValues[rMax]

#Set the chart data
ChartData1_Plot <-ChartData1[,c("xDateValues","Week","yValues")]
ChartData1_Plot$Statistic<-paste("Past YR at ", MaxDate, sep="")


MedianVal<-median(dfTemp$yValues)
MeanVal<-mean(dfTemp$yValues)
stDev<- sd(dfTemp$yValues)
#ribbon to show one st. Dev. 
Ribbon<-data.frame(ChartData1[,c("xDateValues")])
Ribbon$Lower<-MeanVal-stDev
Ribbon$Higher<-MeanVal+stDev
colnames(Ribbon)<-c("xDateValues", "Lower", "Higher")
Ribbon$mean<-ChartData1$mean


#Set the seasons for charting
#Spring March 20, 2013
dSpring <- as.Date(paste("03/20/",maxYR, sep=""), "%m/%d/%Y")
if (MaxDate<=dSpring) { 
    dSpring <- as.Date(paste("03/20/",maxYR-1, sep=""), "%m/%d/%Y")
}  

#summer June 21, 2013
dSummer<-as.Date(paste("06/21/",maxYR, sep=""), "%m/%d/%Y")
if (MaxDate<=dSummer) { 
    dSummer<- as.Date(paste("06/21/",maxYR-1, sep=""), "%m/%d/%Y")
}  
#Autumn September 22, 2013 
dAutumn<-as.Date(paste("09/23/",maxYR, sep=""), "%m/%d/%Y")
if (MaxDate<=dAutumn) { 
    dAutumn<- as.Date(paste("09/23/",maxYR-1, sep=""), "%m/%d/%Y")
}  

# winter December 21, 2013
dWinter<-as.Date(paste("12/21/",maxYR, sep=""), "%m/%d/%Y")
if (MaxDate<=dWinter) { 
    dWinter<- as.Date(paste("12/21/",maxYR-1, sep=""), "%m/%d/%Y")
}  

ChartData_Plot <- ChartData1_Plot


p1<-ggplot(ChartData_Plot, aes(x=xDateValues,y=yValues))+
    geom_line(aes(group=Statistic, colour=Statistic))+
    scale_color_manual(values=c("black"))+
    geom_ribbon(data=Ribbon, aes(group = 1, y=mean, x=xDateValues, ymin=Lower, ymax=Higher), alpha=0.1, fill="blue")+
    geom_hline(aes(yintercept=MinVal), color="red", linetype="dashed")+
    geom_hline(aes(yintercept=MaxVal), color="red", linetype="dashed")+
    annotate(geom="text", x = LableDateMinMax, y = MinVal-MaxVal/90, label = paste("Min as at ", MinD, sep=""), colour = "red", size = 4)+
    annotate(geom="text", x = LableDateMinMax, y = MaxVal+MaxVal/40, label = paste("Max as at ", MaxD, sep=""), colour = "red", size = 4)+
    geom_hline(aes(yintercept=MedianVal), color="darkgreen", linetype="dashed")+
    geom_hline(aes(yintercept=MeanVal), color="blue", linetype="dashed")+
    annotate(geom="text", x = LableDateMinMax, y = MeanVal+MaxVal/40, label = paste("Mean", sep=""), colour = "blue", size = 4)+
    annotate(geom="text", x = LableDateMedian, y = MedianVal+MaxVal/40, label = paste("Median", sep=""), colour = "darkgreen", size = 4)+
    theme(legend.position="bottom")+
    geom_vline(xintercept = as.numeric(dSpring),colour="darkgrey")+
    geom_vline(xintercept = as.numeric(dSummer),colour="darkgrey")+
    geom_vline(xintercept = as.numeric(dAutumn),colour="darkgrey")+
    geom_vline(xintercept = as.numeric(dWinter),colour="darkgrey")+
    annotate(geom="text", x = c(dWinter+45, dSpring+45, dSummer+45, dAutumn+45), y = MaxVal+MaxVal/10, label = c("Winter",
                "Spring", "Summer", "Autumn"), colour = "darkgrey",
                size = 4)+
    ggtitle(bquote(atop(.(titleChart), atop(italic(.(subtitleChart)), ""))))+
    labs(x = "")+
    scale_x_date(breaks="4 weeks",labels = date_format("%b-%Y"))+
    scale_y_continuous(labels = comma)+expand_limits(y = 0)+
    theme(axis.text.x  = element_text(size=10,angle=45,colour="black",vjust=1,hjust=1))+
    labs(y = yAxisTitle)+
    theme(legend.position="none") 




    Footnote<-"Note: Shaded area represents one standard deviation from the mean"

#p1<-arrangeGrob(p1, sub = textGrob(Footnote, x = 0, hjust = -0.1, vjust=0.1, gp = gpar(fontface = "italic", fontsize = 10)))




return(p1)
}

Answer 1

I have figured out the problem. I have not used environment before but it was a very simple fix.

To get the function to work:

.e <- environment() #at the start of the function

...

 ggplot(ChartData_Plot, aes(x=xDateValues,y=yValues), environment = .e)

Local Variables Within aes

For a discussions on environments see:

http://www.r-bloggers.com/environments-in-r/

http://adv-r.had.co.nz/Environments.html

Answer 2

The function geom_hline is looking for MinVal inside the ChartData_Plot data frame, where it does not exist. Add data = NULL to the geom_hline functions and it should be able to find the value.