Manipulate function with variable number of controls - r

Question

My objective is to have a function that can be called with an array of n datasets. This function will call manipulate and create a plot with a control box. This box will have as many checkboxes as there are datasets (i.e. n). Each checkbox will allow to show/hide the corresponding dataset on the plot.
For the purpose of keeping it simple, I will assume each dataset is a simple string instead.
manipulate works fine when the controls are known. Here, for a single control:
manipulate(plot(0,0,main=b), b=checkbox(TRUE, 'bool'))
However, in my case I need a variable number of controls. I'm able to create a list of controls like so:
dataList = c('a', 'b', 'c')
ctrls = list()
for(data in dataList) {
ctrls[[data]] = checkbox(TRUE, data)
}
manipulate(plot(0,0), ctrls)
Now let's see a minimal use case : a function that will create a plot. Its title will be the concatenation of all dataset names which have the value TRUE.
My initial idea was to pass the list of controls to the function, so I can access each control there.
foo <- function(dataList, ctrls) {
print(dataList)
title = ''
for(data in dataList) {
if (ctrls[[data]]) { # this fails
title=cat(title, data)
}
}
plot(0,0,main=title)
}
manipulate(foo(dataList, ctrls), ctrls)
The above fails because ctrls[[data]] is not the value of the control.
Is there a way to access the current value of a control when it's given to manipulate inside a list?

Answer 1

After some fiddling around I found that I could utilize the get function to retrieve the variables' values from the scope before calling foo.
Firstly, I prepare the list of controls
series = list('a', 'b', 'c')
controls = list()
for(data in series) {
controls[[data]] = checkbox(TRUE, data)
}
Then we have the callback function which takes a list as argument
foo <- function(data, bools) {
t=""
for(i in seq_along(data)) {
if(bools[[i]]) t = c(t, data[[i]])
}
plot(0,0,main=t)
}
Finally there's the call to manipulate. Notice I'm mapping the list of series names with their corresponding checkbox's state (TRUE or FALSE).
manipulate(
foo(lapply(series, function(e) get(e))),
controls
)