app.R

library(shiny)

# dummy list of dataframes
test <- data.frame("A" = NA, "B" = NA, "X" = NA)
test2 <- data.frame("D" = NA, "E" = NA, "F" = NA)
test3 <- data.frame("G" = NA, "H" = NA, "X" = NA)
combined_tests <- list(test = test, test2 = test2, test3 = test3)

# Turn list of dataframes into buckets of draggable blocks
rowBlock <- function(name) {
  tags$li(
    class = "block", id = name,
    div(name))
}
rowPallete <- function(data) {
  Map(function(x, y) 
    div(h5(x), tags$ul(class = 'all_blocks', lapply(colnames(y), rowBlock))),
    names(data),
    data)
}
rowArea <- function(bins) {
  column(1, offset = 0, style='padding:0px;',
         rowPallete(bins)
  )
}

ui <- fluidPage(
  tags$head(
    tags$link(rel = "//code.jquery.com/ui/1.12.1/themes/base/jquery-ui.css"),
    tags$script(src = "https://code.jquery.com/ui/1.12.1/jquery-ui.js"),
    tags$link(href = "styles.css", rel = "stylesheet")
  ),
  
  fluidRow(
    column(6, div(h1("Reactive, Can't Sort"), uiOutput("all_rows"))),
    column(6, div(h1("Using script.js"), rowArea(combined_tests)))),
  actionButton("do", "Do"),
   tags$script(src = "script.js")
)

server <- function(input, output) {
  output$all_rows <- renderUI({
    input$do
    one <- data.frame(x = NA, y = NA, z = NA)
    names(one) <- sample(letters, 3)
    two <- data.frame(x = NA, y = NA, z = NA)
    names(two) <- sample(letters, 3)
    rowArea(list(one = one, two = two))
  })
  
}

shinyApp(ui = ui, server = server)

script.js

$(function() {
  $(".all_blocks").sortable();
  $(".all_blocks").disableSelection();
  
  $('#all_rows').on('shiny:value', function() {
    // whenever the input changes, re-run sortable
    // with a small delay to the let the DOM update after shiny:value completes
    setTimeout(() => $('#all_rows .all_blocks').sortable().disableSelection(), 1)
  })
});

styles.css

#block {
list-style-type: none;
margin: 0;
padding-bottom: 2px;
}

ul {
    list-style: none;
    padding-left: 0;
}

li {
  list-style-type: none;
  padding-bottom: 2px;
}


.all_blocks li,
#block li {
border: 1px solid lightgray;
border-radius: 15px;
margin-bottom: 2px;
padding-left: 3px;
text-align: center;
}