$ operator for variable object names - r

Question

I am trying to use the $ operator for selecting and reformating specific columns in a for loop on variably created data.frame objects. I tried 4 different solutions in my commented code, but none of them works. I looked all over SO but i don't seem to find another solution to try.
How can i make use of the $ operator to select specific columns with variable data.frame names?
Thanks
weather_data_files<-c("CMC","ECMWF","ECMWF_VAR_EPS_MONTHLY_FORECAST",
"GFS","ICON_EU","UKMET_EURO4")
for(filename in weather_data_files){
#create data frame environment objects
assign(paste(filename),read.csv(file = paste(filename,".csv",sep = ""),sep = ";"))
#first solution does not work, because filename is here an atomic vector
#rather than a data.frame
#ErrorMessage: $ operator is invalid for atomic vectors
filename$Forecast.Time<- as.POSIXct(filename$Forecast.Time,
format="%d.%m.%Y %H:%M+%S",tz="UTC")
#ok get it, let's try second soltution,but
#it also does not work allthough i try to get the data.frame object
#ErrorMesssage: could not find function "get<-
get(filename)$Forecast.Time<-
as.POSIXct(get(filename)$Forecast.Time,format="%d.%m.%Y %H:%M+%S",tz="UTC")
#Third solution as.name also does not work
#ErrorMessage: object of type 'symbol' is not subsettable
as.name(filename)$Forecast.Time<-
as.POSIXct(as.name(filename)$Forecast.Time,format="%d.%m.%Y %H:%M+%S",tz="UTC")
#Fourth solution comparable to second solution, still not working
#ErrorMessage: could not find function "eval<-"
eval(assign(filename,get(filename)))$Forecast.Time<-
as.POSIXct(eval(assign(filename,get(filename)))$Forecast.Time,
format="%d.%m.%Y %H:%M+%S",tz="UTC")
}

Answer 1

So, the problem is you're passing in character strings, not objects. The get function retrieves the object, just doesn't have a place to store it.
You could always load the character string into a temporary variable as you're looping. Operate on the temporary variable and then assign when you're done.
for(filename in c("a","b")){
tmp <- get(filename)
}
You could also skip most of the for loop and use the apply family.
files = lapply(paste(c("CMC","ECMWF","ECMWF_VAR_EPS_MONTHLY_FORECAST",
"GFS","ICON_EU","UKMET_EURO4"),".csv",sep=""),
read.csv,sep=";")
files = lapply(files,function(x){x$Forecast.Time = as.POSIXct(x$Forecast.Time,
format="%d.%m.%Y %H:%M+%S",tz="UTC");return(x)}
Now you have a list of your files you can work on. You could assign them to global variables if you want.