Shiny reactive Unexpected Behavior - r

Question

I'm trying to create a reactive function that looks up the indices, corresponding to the user's inputs, from a dataframe referred to as df in the code below. Just to give you an idea, here's how the dataframe df looks like:
'data.frame': 87 obs. of 6 variables:
$ Job : Factor w/ 66 levels "Applications Engineer",..: 61 14 23 31 22 15 57 26 30 13 ...
$ Company : Factor w/ 102 levels "A10 Networks",..: 95 50 83 71 80 60 20 7 30 51 ...
$ Location: Factor w/ 64 levels "Ayr","Bangalore",..: 36 22 19 29 59 7 7 55 53 63 ...
$ Posted : num 2 3 2 3 1 1 2 5 4 1 ...
$ Source : Factor w/ 2 levels "Glassdoor","Indeed": 2 2 2 2 2 2 2 2 2 2 ...
$ url : chr "http://ca.indeed.com/rc/clk?jk=71f1abcd100850c6" "http://ca.indeed.com/rc/clk?jk=504724a4d74674fe" "http://ca.indeed.com/rc/clk?jk=d2e78fb67e8c86d6" "http://ca.indeed.com/rc/clk?jk=df790aa5fc7bdc3c" ...
The reactive function mostly uses the grep function to do a text search and find the respective indices. Here's the relevant chunk of the code from server.R:
#Create a reactive function to look up the indices correponding to the inputs
index <- reactive({
ind.j <- if(input$j=='') NULL else grep(input$j,df[,'Job'],ignore.case = T)
ind.c <- {tmp<-lapply(input$c, function(x) {which(df[,'Company']==x)}); Reduce(union,tmp)}
ind.l <- if(input$l=='') NULL else grep(input$l,df[,'Location'],ignore.case = T)
ind.d <- which(df[,'Posted']<=input$d)
ind.s <- {tmp<-lapply(input$s, function(x) {which(df[,'Source']==x)}); Reduce(union,tmp)}
ind.all <- list(ind.j,ind.c,ind.l,ind.d,ind.s)
ind <- if(is.null(ind.s)) NULL else {ind.null<- which(lapply(ind.all,is.null)==TRUE) ;Reduce(intersect,ind.all[-ind.null])}
})
I have printed the results of ind.j, ind.c, ind.l,ind.d, ind.s, and ind.all to the console and they all produce the right results. however when I test the results of ind it's not quite what I expect so I'm wondering if it's the reactivity or the line of code that doesn't work.
What the ind intends to do is to take the list of all the looked-up indices, stored in ind.all, and applies the intersect function recursively to find the common elements from all the sublists in ind.all.
The index function works fine for individual filters. however when I enter values for all the indices, the function does not update to the correct list of indices as expected.

Answer 1

This question has been answered by in this post by jdharrison. I'm going to reiterate his answer here:
The problem you have is with the which function:
> which(rep(FALSE, 5))
integer(0)
You can change:
ind <- if(is.null(ind.s)){
NULL
}else{
ind.null<- which(lapply(ind.all,is.null)==TRUE)
Reduce(intersect,ind.all[-ind.null])
}
to
ind <- if(is.null(ind.s)){
NULL
}else{
Reduce(intersect,ind.all[!sapply(ind.all,is.null)])
}