Troubles using "selectInput" to select variable with dplyr

[Ignacio Martinez]

Hi,

This very simple example illustrates the problem that I'm having:

    df1 <-

      structure(

        list(

          `long name 1` = c(NA, 18L, NA, 24L, 21L, NA, NA,NA, NA, NA),

          `long name 2` = c(NA, 24L, NA, 35L, 23L, NA, NA,NA, NA, 25L)

        ), class = c("tbl_df", "data.frame"),

        row.names = c(NA,-10L), .Names = c("long name 1", "long name 2")

      )

    

    server <- function(input, output) {

      output$txt1 <- renderText({

        df1 %>% summarise(y1 = mean(input$select,na.rm = T)) %>%

          as.character()

      }) 

    }

    

    ui <- fluidPage(sidebarLayout(sidebarPanel(

      width = 3,

      selectInput(

        "select", label = h3("Variable"),

        choices = list("long name 1" = "long name 1",

                       "long name 2" = "long name 2"),

        selected = 1

      )

    ),

    mainPanel(h3(textOutput(

      "txt1"

    )))))

    

    shinyApp(ui = ui, server = server)

The only solution that I can think is to use a series of if statements instead of using input$select directly in summarise. Any suggestions?

Thanks!

[msquatrito]

Hi, 

you could use  `substitute` and `eval`, such as:

server <- function(input, output) {
  output$txt1 <- renderText({

    txt <- substitute(df1 %>%
                        summarise(y1 = mean(sel,na.rm = T)) %>%
                        as.character(),
                      list(sel = as.name(input$select)))
    txt <- eval(txt)
  })
}

Best,

Massimo

[Winston Chang]

You can use the `summarise_` function when you want to use variables in dplyr functions. Other dplyr functions also have a version with a trailing underscore. For example:

library(dplyr)

# The usual way of using dplyr

mtcars %>%

  group_by(cyl) %>%

  summarise(meanwt = mean(wt))

# Passing in strings in variables

group <- "cyl"

var <- "mean(wt)"

mtcars %>%

  group_by_(group) %>%

  summarise_(meanwt = var)

See https://cran.r-project.org/web/packages/dplyr/vignettes/nse.html for more information.

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