Convert factor levels into lists for use in dynamic input in R Shiny

Question

I'm trying to convert factor levels output into a list so I can create a dynamic input for a SelectInput function in R Shiny.

Basically, I import a CSV file, and would like to create the drop-down list in SelectInput by using the "categories" (levels) in the first column of the CSV file.

So, in UI.R I have:

uiOutput("categoryPicker")

And in server.R I have:

datatwo <- read.csv(file="data2.csv",head=TRUE,sep=",")

then, in the "shinyServer(function(input, output)" section ("category" is a header in the CSV file, by the way):

output$categoryPicker <- reactiveUI(function() {
categories <- levels(datatwo$category)
selectInput("category", "Category:", categories)
})

This doesn't work, gives me the following error:

Error in choices[[choiceName]] : subscript out of bounds

The str(categories) output is as follows:

chr [1:22] "" "Cat1" "Cat2" "Cat3" "Cat4" "Cat5" ...

If I do "list(levels(datatwo$category)", it just gives me one drop down, which is the entire str(categories) output:

List of 1 $ : chr [1:22] "" "Cat1" "Cat2" "Cat3" ...

I'm trying to get this in the form of (such that when str(x) is done the output would be):

List of X
$ Cat1: chr "Cat1"
$ Cat2: chr "Cat2"
$ Cat3: chr "Cat3"
...

But I'm not sure how to do this. I'm also not sure why the first item is a "" [empty string]. I'm pretty new to R and Shiny so forgive my ignorance, but any help would be greatly appreciated.

BTW, I've been working off this tutorial: http://rstudio.github.com/shiny/tutorial/#dynamic-ui

Thanks.

Answer 1

I don't know if the names in the list are important or not, but this should give you what you want:

setNames(as.list(categories), categories)