Change column name of a reactive data frame in shiny R

Question

I have a code that looks something like this:

d_frame<-reactive(unique(as.data.frame(do.call("rbind", sapply(1:(length(intarr())), 
FUN = function(i) c(substr(readlinesop()
[intarr()[i]+1],17,26),substr(readlinesop()[intarr()[i]+2],17,26)), simplify = FALSE)))))

bv<-reactive(ncol(d_frame()))
colnames(d_frame) <- c("Sand", "Water")
subset_dataset <-eventReactive(input$go, {d<-bv()})

The first line which has the output d_frame creates a data frame. When I try to change the column name of this it throws an error :

So, I tried to find the number of columns in the d_frame using ncol as mentioned above which returned 2. But, I don't know what's causing the error. Can you please help me with this?

Your `d_frame` is a function hence and all updates need to be within reactive expression or observer — Pork Chop, Nov 29 '16 at 18:16
@PorkChop: I changed as mentioned as below, but still no luck. Can you please help. I am a newbie to R shiny. — Aizen, Nov 30 '16 at 08:14

score 1 · Accepted Answer · edited Nov 01 '17 at 16:46

1

Try something like this. Note that the d_frame() is a reactive function. In your calculations you will use d_frame2()

 d <- NULL
 d_frame <-
   reactive(unique(as.data.frame(do.call(
     "rbind", sapply(
       1:(length(intarr())),
       FUN = function(i)
         c(substr(readlinesop()
                  [intarr()[i] +
                      1], 17, 26), substr(readlinesop()[intarr()[i] + 2], 17, 26)),
       simplify = FALSE
     )
   ))))

 bv <- reactive(ncol(d_frame()))
 d_frame2 <- reactive({
   testdata <- d_frame()
   colnames(testdata) <- c("Sand", "Water")
   testdata
 })

 subset_dataset <- eventReactive(input$go, {
   d <<- bv()
 })

edited Nov 01 '17 at 16:46

user5249203

4,436
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answered Nov 30 '16 at 08:29

Pork Chop

28,528
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It gives error: "Error in <-: invalid (NULL) left side of assignment". If I remove () from d_frame in colnames(d_frame()) <- c("Sand", "Water"), I again get the same error what I mentioned in my question. – Aizen Nov 30 '16 at 08:52
I don't know exactly how you're constructing your dataframe `d_frame()` you will need to give more code that include the `intarr()` and `readlinesop()` – Pork Chop Nov 30 '16 at 08:53
This works!! Thanks. But can you please explain what was causing the error? – Aizen Nov 30 '16 at 08:58
1

I don't think we can directly change the column names of a reactive function, you have to put the contents into a variable first – Pork Chop Nov 30 '16 at 09:04

score 0 · Answer 2 · edited Nov 01 '17 at 16:47

0

In your example, d_frame is a reactive function returning a data.frame, not a data.frame itself.

You can set its column names when you build it:

d_frame <-
   reactive(unique(as.data.frame(
     do.call("rbind", sapply(
       1:(length(intarr())),
       FUN = function(i)
         c(substr(readlinesop()[intarr()[i] + 1], 17, 26),
           substr(readlinesop()[intarr()[i] + 2], 17, 26)),
       simplify = FALSE
     )), col.names <- c("Sand", "Water")
   )))

edited Nov 01 '17 at 16:47

EvilTak

7,091
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answered Nov 29 '16 at 18:17

HubertL

19,246
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I added the col.names as mentioned above but I still couldn't see the column names, it is still coming as V1 & V2. Further code is something like this: subset_dataset <-eventReactive(input$go, {d_frame()}) – Aizen Nov 29 '16 at 18:30
Any more info on this? – Aizen Nov 30 '16 at 08:15

Change column name of a reactive data frame in shiny R

2 Answers2