I am working on a shiny app which contains a list of dataframes (table_list
) and below is a reactive function assignment from that app. There is an input value input$column_names
which is a list of column names that correspond to the column names in table_list
. I want to reactively select these columns within a lapply()
function using the column names. Below is my failed attempt.
Selected_column <- reactive({
req(table_list())
lapply(table_list, function(DT){
DT$input$column_name
})
})
The line DT$input$column_name
returns a NULL value. So my question is, how can I select a column of a given list dataframe based on a column name input?
CodePudding user response:
That's not specific to shiny. To access or extract a column from a dataframe (or a list
or ... ) whose name is stored in a variable you have to use [[
instead of $
.
For more see e.g. The difference between bracket [ ] and double bracket [[ ]] for accessing the elements of a list or dataframe
column_name <- "mpg"
# Does not work
mtcars$column_name
#> NULL
# Works
mtcars[[column_name]]
#> [1] 21.0 21.0 22.8 21.4 18.7 18.1 14.3 24.4 22.8 19.2 17.8 16.4 17.3 15.2 10.4
#> [16] 10.4 14.7 32.4 30.4 33.9 21.5 15.5 15.2 13.3 19.2 27.3 26.0 30.4 15.8 19.7
#> [31] 15.0 21.4
And a minimal shiny app based on the code snippet you provided:
library(shiny)
ui <- fluidPage(
selectInput("column_name", "Select a column:", choices = names(mtcars)),
tableOutput("selected")
)
server <- function(input, output, session) {
table_list <- reactive(
list(
a = mtcars,
b = mtcars
)
)
Selected_column <- reactive({
req(table_list())
lapply(table_list(), function(DT) {
DT[[input$column_name]]
})
})
output$selected <- renderTable({
head(rbind.data.frame(Selected_column()))
})
}
shinyApp(ui, server)
#>
#> Listening on http://127.0.0.1:8179