Why does Rshiny tableOutput create an additional column?

Question

Hi all I'm relatively new to Rshiny and got some unexpected behavior in a simple example of tableOutput.

I'm trying to display a simple table in an Rshiny application but notice there is an additional column created that I did not specify. I'm a little baffled as reproducing the code in 'normal' R does not show this additional column.

My RShiny code:

library(shiny)


ui <- fluidPage(


titlePanel("Test"),
tableOutput("Table1")

)


server <- function(input, output) {

output$Table1 <- renderTable({
matrix1 = matrix(c(2, 3, 5, 8, 13), ncol =1, nrow = 5)
rownames(matrix1) = c('Min', 'value1', 'Max', 'value2', 'Standard deviation')
colnames(matrix1) = c('values')
as.table(matrix1)
})
}


shinyApp(ui = ui, server = server)

This results in the following app where the 'Var2' column is the one I did not expect: RShiny view

I expected the output to be similar of the 'normal' R one: R table Created by this R code:

matrix1 = matrix(c(2, 3, 5, 8, 13), ncol =1, nrow = 5)
rownames(matrix1) = c('Min', 'value1', 'Max', 'value2', 'Standard deviation')
colnames(matrix1) = c('values')
table1 = as.table(matrix1)

Can someone help me understand from where the additional column comes from in the RShiny view and how to get rid of it?

(Ps: I'm new to posting, so please let me know in case I'm unclear/missed something)

Answer 1

It is a table object, instead wrapped around the matrix, which is really not needed, instead it can be just the matrix object or converted to data.frame

server <- function(input, output) {
  
  output$Table1 <- renderTable({
    matrix1 = matrix(c(2, 3, 5, 8, 13), ncol =1, nrow = 5)
    rownames(matrix1) = c('Min', 'value1', 'Max', 'value2', 'Standard deviation')
    colnames(matrix1) = c('values')
    matrix1
  }, rownames = TRUE)
}
shinyApp(ui = ui, server = server)

-output

---

When we add as.table, it converts to table class and it gets converted to data.frame during the process and this results in the change of format

> as.table(matrix1)
                   values
Min                     2
value1                  3
Max                     5
value2                  8
Standard deviation     13
> as.data.frame(as.table(matrix1))
                Var1   Var2 Freq
1                Min values    2
2             value1 values    3
3                Max values    5
4             value2 values    8
5 Standard deviation values   13

> str(as.table(matrix1))
 'table' num [1:5, 1] 2 3 5 8 13
 - attr(*, "dimnames")=List of 2
  ..$ : chr [1:5] "Min" "value1" "Max" "value2" ...
  ..$ : chr "values"

If we check the source code of renderTable, there is a line which does the as.data.frame and thus it changes the format to three column because there are different methods for as.data.frame depending on the class of the object

> shiny::renderTable
...
classNames <- paste0("table shiny-table", paste0(" table-", 
            names(format)[format], collapse = ""), paste0(" spacing-", 
            spacing))
data <- as.data.frame(data)
...

Also, check methods for as.data.frame

> methods(as.data.frame)
 [1] as.data.frame.aovproj*            as.data.frame.array               as.data.frame.AsIs                as.data.frame.character          
 [5] as.data.frame.complex             as.data.frame.data.frame          as.data.frame.data.table*         as.data.frame.Date               
 [9] as.data.frame.default             as.data.frame.descr*              as.data.frame.difftime            as.data.frame.EventHistory.frame*
[13] as.data.frame.factor              as.data.frame.ftable*             as.data.frame.function*           as.data.frame.grouped_df*        
[17] as.data.frame.groupedData*        as.data.frame.idf*                as.data.frame.integer             as.data.frame.ITime*             
[21] as.data.frame.list                as.data.frame.logical             as.data.frame.logLik*             as.data.frame.mapped_discrete*   
[25] as.data.frame.matrix              as.data.frame.model.matrix        as.data.frame.noquote             as.data.frame.numeric            
[29] as.data.frame.numeric_version     as.data.frame.ordered             as.data.frame.POSIXct             as.data.frame.POSIXlt            
[33] as.data.frame.raw                 as.data.frame.resamples*          as.data.frame.shingle*            as.data.frame.Surv*              
[37] as.data.frame.Surv2*              as.data.frame.table    #####           as.data.frame.tbl_df*             as.data.frame.timeDate*          
[41] as.data.frame.ts                  as.data.frame.vctrs_sclr*         as.data.frame.vctrs_vctr*         as.data.frame.vector             
[45] as.data.frame.xyVector*          
see '?methods' for accessing help and source code

The source code of as.data.frame.table does create three columns

> as.data.frame.table
function (x, row.names = NULL, ..., responseName = "Freq", stringsAsFactors = TRUE, 
    sep = "", base = list(LETTERS)) 
{
    ex <- quote(data.frame(do.call("expand.grid", c(dimnames(provideDimnames(x, 
        sep = sep, base = base)), KEEP.OUT.ATTRS = FALSE, stringsAsFactors = stringsAsFactors)), 
        Freq = c(x), row.names = row.names))
    names(ex)[3L] <- responseName
    eval(ex)
}