Trying to use SelectInput to sum from a data frame - r

Question

Reformulating my question, I´m trying to synthetize a data frame reactively, with a selectinput = c("col_1","col_2","col_3","col_4","col_5")
My dataframe looks something like this
Date . Store_ID . Sales . Stock . ETC
I need to be able to sum all the data in the same stores, with the different user selected columns.
Using the mtcars dataframe as an example to work with, my objective is to have a table like this
SelectInput = disp
cyl - disp
4 - sum(every 4 cylinders disp)
6 - sum(every 6 cylinders disp)
8 - sum(every 8 cylinders disp)
SelectInput = qsec
cyl . qsec
4 . sum(every 4 cylinders qsec)
6 . sum(every 6 cylinders qsec)
8 . sum(every 8 cylinders qsec)
library(shiny)
library(tidyverse)
ui <- bootstrapPage(
selectInput(
"col",
"Column",
colnames(mtcars),
selected = "mpg"),
plotOutput("histCentile", height = 200)
)
server <- function(input, output) {
data <- reactive({
mtcars() %>%
group_by(cyl = cyl) %>%
pull(input$col) %>%
sum()
})
output$histCentile <- renderPlot({
hist(data()$[[input$col]],
main = "Graph",
xlab = "Units",
xlim = range(data()$[[input$col]]),
col = '#00DD00',
border = 'white')
})
}
# Run the application
shinyApp(ui = ui, server = server)

Answer 1

I'm not sure what you're trying to do but here is a minimal reproducible example using reactive to filter data based on the selectInput variable.
library(shiny)
library(tidyverse)
ui <- bootstrapPage(
selectInput(
"col",
"Column",
colnames(mtcars),
selected = "mpg"),
textOutput("selected_col")
)
server <- function(input, output) {
data <- reactive({
mtcars %>% pull(input$col) %>% sum()
})
output$selected_col <- renderText({
sprintf("The sum of column %s is %f", input$col, data())
})
}
# Run the application
shinyApp(ui = ui, server = server)
Explanation: In data we sum the values from input$col based on the selectInput selection. data is therefore a reactive value, which we show in output$selected_col.
Update
There are a few issues with your updated code example:
In the reactive block, you're summarising data to give a single number. Plotting a histogram based on a single number makes no sense. Secondly, there is a typo: it should be mtcars not mtcars(); and lastly, group_by(cyl = cyl) is unnecessary as you don't do any group-wise calculation afterwards (it should also be group_by(cyl)).
You don't actually need a reactive block here at all, since you can do the filtering in renderPlot directly but I guess that is a matter of personal preference.
The following dynamically updates a histogram based on the selected column from selectInput
library(shiny)
library(tidyverse)
ui <- bootstrapPage(
selectInput(
"col",
"Column",
colnames(mtcars),
selected = "mpg"),
plotOutput("histo")
)
server <- function(input, output) {
data <- reactive({
mtcars %>% pull(input$col)
})
output$histo <- renderPlot({
hist(data())
})
}
# Run the application
shinyApp(ui = ui, server = server)

Answer 2

Update - Solution
Thanks to Maurits Evers help, and some research, I managed to do what I wanted to
library(shiny)
library(tidyverse)
ui <- bootstrapPage(
selectInput(
"col",
"Column",
colnames(mtcars),
selected = "mpg"),
plotOutput("histo")
)
server <- function(input, output) {
data <- reactive({
Graphby <- input$col
with(mtcars,aggregate(qsec,list(cyl=cyl),sum))
aggregate(mtcars[[Graphby]],list(cyl=mtcars$cyl),sum)
})
output$histo <- renderPlot({
hist(data()$x)
})
}
# Run the application
shinyApp(ui = ui, server = server)
What it does is an interactive histogram by merging groups of data like this
in a reactive way, by choosing different columns.