R Shiny: Computing new Variables selected by "selectInput" - r

Question

I'm working on a dashbord with Shiny and want to compute new variables based on the selected Variabels by selectInput.
Comparable to this in normal R-Code:
library(dplyr)
new_df <- old_df %>% mutate(new_1 = old_var1 + old_var2)
I'm able to compute new values with the sliderInput, but this are only single values. I want to compute a hole new variable with all the oppertunities of displaying the new variable in Tables and graphics.
Please try the followring syntax (the data is online avalible).
As you mentioned, all Inputs are working as they should.
library(shiny)
library(readr)
library(ggplot2)
library(stringr)
library(dplyr)
library(DT)
library(tools)
load(url("http://s3.amazonaws.com/assets.datacamp.com/production/course_4850/datasets/movies.Rdata"))
ui <- fluidPage(
sidebarLayout(
# Inputs
sidebarPanel(
h3("Plotting"), # Third level header: Plotting
# Select variable for y-axis
selectInput(inputId = "y",
label = "Y-axis:",
choices = c("IMDB rating" = "imdb_rating",
"IMDB number of votes" = "imdb_num_votes",
"Critics Score" = "critics_score",
"Audience Score" = "audience_score",
"Runtime" = "runtime"),
selected = "audience_score"),
# Select variable for x-axis
selectInput(inputId = "x",
label = "X-axis:",
choices = c("IMDB rating" = "imdb_rating",
"IMDB number of votes" = "imdb_num_votes",
"Critics Score" = "critics_score",
"Audience Score" = "audience_score",
"Runtime" = "runtime"),
selected = "critics_score"),
# Select variable for color
selectInput(inputId = "z",
label = "Color by:",
choices = c("Title Type" = "title_type",
"Genre" = "genre",
"MPAA Rating" = "mpaa_rating",
"Critics Rating" = "critics_rating",
"Audience Rating" = "audience_rating"),
selected = "mpaa_rating"),
hr(),
# Set alpha level
sliderInput(inputId = "alpha",
label = "Alpha:",
min = 0, max = 1,
value = 0.5),
# Set point size
sliderInput(inputId = "beta",
label = "Beta:",
min = 0, max = 5,
value = 2)
),
# Output:
mainPanel(plotOutput(outputId = "scatterplot"),
textOutput(outputId = "description"),
DT::dataTableOutput("moviestable"))
)
)
server <- function(input, output, session) {
output$scatterplot <- renderPlot({
ggplot(data = movies, aes_string(x = input$x, y = input$y,
color = input$z)) +
geom_point(alpha = input$alpha, size = input$beta) +
labs(x = toTitleCase(str_replace_all(input$x, "_", " ")),
y = toTitleCase(str_replace_all(input$y, "_", " ")),
color = toTitleCase(str_replace_all(input$z, "_", " ")))
})
vals <- reactiveValues()
observe({
vals$x <- input$alpha
vals$y <- input$beta
vals$sum <- vals$x + vals$y
})
output$description <- renderText({
paste0("Alpha: ",input$alpha, " Beta:", input$beta," and the sum of alpha and beta:",vals$sum, ".")
})
output$moviestable <- DT::renderDataTable({
DT::datatable(data = movies,
options = list(pageLength = 10),
rownames = FALSE)
})
}
shinyApp(ui = ui, server = server)
I tried different ways to solve this problem:
1st try:
vals2 <- reactiveValues()
observe({
vals2$x <- input$y
vals2$y <- input$x
vals2$sum <- vals2$x + vals2$y
})
output$description2 <- renderText({
paste0("Input y: ",input$y, " Input x:", input$x," and the sum of both variables is:",vals2$sum, ".")
})
Warning: Error in +: non-numeric argument to binary operator
Stack trace (innermost first):
56: observerFunc [C:/Users/XXXXXX/Desktop/app.R#110]
1: runApp
ERROR: [on_request_read] connection reset by peer
2nd try:
output$try2 <- renderUI({
movies_2 <- movies %>% mutate(new_1 = input$y + input$x)
})
output$moviestable2 <- DT::renderDataTable({
DT::datatable(data = movies_2,
options = list(pageLength = 10),
rownames = FALSE)
})
Warning: Error in inherits: object 'movies_2' not found
I've no idea where I what I can try next...
I'm very happy for every kind of help!

Answer 1

You should make movies_2 in a reactive. Your output$try2 won't work because its expecting UI objects.
To match the call you make on the UI side I've renamed back to moviestable and have changed input$x + input$y to paste0(input$y, input$x) since they are both character.
movies_2 <- reactive({
movies %>% mutate(new_1 := movies[[input$x]] + movies[[input$y]])
})
output$moviestable <- DT::renderDataTable({
DT::datatable(data = movies_2(),
options = list(pageLength = 10),
rownames = FALSE)
})