Why does Rshiny tableOutput create an additional column? - r

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)
}