Formatting reactive data.frames in Shiny
r, shiny
Solution
I am responding to my own question largely to say that I was being a nincompoop. Once the file is read in using `reactiveFileReader()` it becomes a "reactive source". As explained in the shiny tutorial here the reactive sources are modified from outside - a user entering a new value, or in this case, an update of the file. You can't modify it from inside the `server.r`.
So, for my case I used the `col.names` and `colClasses` options in `read.csv()` to get the original data in the best format that I could. I also made use of the very useful `setAs` function to get `read.csv` to understand how to format the date, as explained here: Specify date format for colClasses argument ... .
From there, any new columns that I needed to create from the data had to be done as a separate object using a reactive function like this:
NewThing<-reactive({ function(MyReacitveCSVdata()$colname) })
And then `NewThing()` in turn can be used however you wish. This is how you can get around issues such as character values in an otherwise numeric column. If you try to just bring it in using `colClasses="numeric"` you will get an error and the `read.csv()` will fail. Instead first import the column as "character" and then use `reactive({})` with `as.numeric()` to assign it to a new object. Be sure to note that the new object cannot be a new column in the `data.frame` you brought in using `reactiveFileReader()`, instead it must be a new object that depends on that `data.frame`.
Problem
I have a working shiny application, but I am changing it so that the input data is reactive - it will update when the underlying data updates. It worked fine when it just read in the data, but now that the data is reactive I am having problems with one of the files (two others work just as expected). The file is a .csv which is exported from a database, and I would like to do a little housekeeping before using - change some names and format some data. The relevant part is: ``` server.r W.Data<-reactiveFileReader(2000,session, "WaterData.csv",read.csv,header=TRUE,as.is=TRUE) ``` This works fine, but then the next two lines won't work: ``` names(W.Data())[names(W.Data())=="Visit_Start_Date"]<-"Visit.Date" W.Data()$Visit.Date<-as.Date(W.Data()$Visit.Date,"%m/%d/%Y") ``` When i run this I get ``` Error in W.Data()$VisitDate <- as.Date(W.Data()$VisitDate, "%m/%d/%Y"): invalid (NULL) left side of assignment ``` and similar for the other line. What is going on here? Can I do these sort of things with a `data.frame` that is read from `reactiveFileInput`? I tried changing the names in the underlying .csv file to have underscores rather than spaces, and I tried putting the `names()` and `as.Date()` in `reactive()` expressions, but these made no difference. Thanks