Using an R function output within another function - r

Question

I am adapting an open-source code from GitHub (https://github.com/PeterDSteinberg/RSWMM) to calibrate EPA-SWMM. The code is written in two parts -- RSWMM.r contains the functions needed to look up/ replace SWMM values, read in the calibration files etc. runRSWMM.r is a wrapper containing the optimization code that calls in the relevant RSWMM functions. I need to edit the RSWMM code to read in a .txt file and have written the following code to do so.
getLIDtimeseriesFromTxt <- function(TxtFile, dateformat = "%m/%d/%y %H:%M"){
#RW (05/12/17): This function added to read in the appropriate CSV file
#containing the LID outputs
library(chron)
LID_data <- read.table(TxtFile, skip=9)
times <- LID_data[,1]
startTime <- as.chron("6/8/2006 1:00", format="%m/%d/%Y %H:%M", tz="GMT") #M/D/YY H:MM
simData <<- {}
simData$times <<- (times/24)+startTime
simData$obs <<- LID_data[,9] #the ninth column is ponding depth
return(simData)
}
getCalDataFromCSV<-function(CSVFile,dateFormat="%m/%d/%y %H:%M"){
temp=read.csv(file=CSVFile, header = TRUE, sep = ",", quote="\"", dec=".", fill = TRUE, comment.char="",stringsAsFactors = FALSE)
calData<<-{}
#RW (05/12/17): This line of code edited to match the date format pulled in from the simulation file.
calData$times<<-as.chron(temp[,1], format=dateFormat,tz="GMT")
calData$obs<<-temp[,2]
return(calData)
}
interpCalDataToSWMMTimes<-function(){
mergedData <- merge(simData, calData, by="times")
return(mergedData)
#first column of mergedData are times as chrons,
#second column is simulated data
#third column is observed data
}
When I run the full code from runRSWMM, I get the error the "simData" is not found, which implies that I cannot use merge. However, this doesn't appear to be a problem with the variable "calData", which I can see in my global environment in RStudio. What is the difference in the way the two variables are being output? How can I fix this error?