Bangyou Bangyou - 1 month ago 10
R Question

How to generate a URL to restore the user input values in Shiny

I have created Shiny app with lots of inputs (parameters). Our users would like to go back with the same input values.

I have checked this example (http://shiny.rstudio.com/articles/client-data.html) which show to get url through session$clientData$url_search, but cannot generate a url from sidebarPanel inputs in the left. For example:

http://localhost:8100/?obs=10


How could generate a URL which could restore the same values in Shiny? A short one should be the best as there are many inputs.

Please let me know if my question is not clear.

Thanks for any suggestions.

Answer

To keep things simple, you don't have to write any code in server.R. Parsing the URL query string (e.g. ?obs=10) and setting the corresponding inputs can be nicely done by just writing some javascript code.

Below I present a simple example where you can see how you can dynamically set the value of any built-in input controls of Shiny.

ui.R

shinyUI(
  fluidPage(
    sidebarLayout(
        sidebarPanel(
            # wrap input controls into a container so that we can use binding.find()
            # function to quickly locate the input controls.
            tags$div(id="input_container", 
                textInput("username", h6("Username:")),
                numericInput("age", h6("Age:"), 
                            min=1, max=99, value=20, step=1),
                selectInput("sex", h6("Sex:"), choices=c("Male", "Female")),
                # load Javascript snippet to parse the query string.
                singleton(tags$script(type="text/javascript", 
                                    src="js/parse_input.js"))  
            )
        ),
        mainPanel(
            verbatimTextOutput("log")
        )
    )
  )
)

server.R

# does nothing but echoes back the user's input values
shinyServer(function(input, output) {
    output$log <- renderPrint({
        paste("Username: ", input$username, "; Age: ", input$age,
              "; Sex: ", input$sex, sep="")
    })
})

www/js/parse_input.js

Finally, you need to create folder www/js under your Shiny project directory, and put this parse_input.js file inside the js folder.

$(document).ready(function() {
    if (window.location.search) {
        var input_params = {};
        /* process query string, e.g. ?obs=10&foo=bar */
        var params = $.map(
            window.location.search.match(/[\&\?]\w+=[^\&]+/g), 
            function(p, i) { 
                var kv = p.substring(1).split("=");
                # NOTE: might have issue to parse some special characters here?
                input_params[kv[0]] = decodeURIComponent(kv[1]);
            }
        );

        /* Shiny.inputBindings.getBindings() return the InputBinding instances
           for every (native) input type that Shiny supports (selectInput, textInput,
           actionButton etc.)  */
        $.each(Shiny.inputBindings.getBindings(), function(i, b) {
            /* find all inputs within a specific input type */
            var inputs = b.binding.find('#input_container');
            $.each(inputs, function(j, inp) {
                /* check if the input's id matches the key specified in the query
                   string */
                var inp_val = input_params[$(inp).attr("id")];
                if (inp_val != undefined) {
                    b.binding.setValue(inp, inp_val);
                }
            });
        });
    }
});

You can then visit the website using URL like http://localhost:7691/?sex=Female&age=44&username=Jane.

You should see that on the main panel, the text becomes:

[1] "Username: Jane; Age: 44; Sex: Female"

EDIT: Create a snapshot of current input values, save it to a local file, and restore it using snapshot ID

Bangyou reminded me that my original answer (above) didn't address his question. So below is my second trial to answer the question.

ui.R

shinyUI(
  fluidPage(
    sidebarLayout(
        sidebarPanel(
            # wrap input controls into a container
            tags$div(id="input_container", 
                textInput("username", h6("Username:")),
                numericInput("age", h6("Age:"), 
                            min=1, max=99, value=20, step=1),
                selectInput("sex", h6("Sex:"), choices=c("Male", "Female")),
                singleton(tags$script(type="text/javascript", 
                                    src="js/parse_input.js"))  
            ),
            tags$button(type="button", id="save_options", 
                        h6("Save current options")),
            tags$input(type="text", style="display:none;", value="{}",
                       id="inputs_snapshot")

        ),
        mainPanel(
            verbatimTextOutput("log"),
            verbatimTextOutput("gen_url")
        )
    )
  )
)

server.R

#  user.saved.snapshots <- list(
#    list(sex="Male", age=32, username="Jason"),
#    list(sex="Male", age=16, username="Eric"),
#    list(sex="Female", age=46, username="Peggy")
#  )
#  
#  save(user.saved.snapshots, file="snapshots.Rdata")

# ^^ Run above code **ONCE** to initiate a dummy data file, storing some possible options. 

load("snapshots.Rdata")

renderRestoration <- function(expr, env=parent.frame(), quoted=F) {
  func <- exprToFunction(expr)
  function() {
    func() 
    # return the selected snapshot to the client side
    # Shiny will automatically wrap it into JSOn
  }
}

shinyServer(function(input, output, session) {
    output$log <- renderPrint({
        paste("Username: ", input$username, "; Age: ", input$age,
              "; Sex: ", input$sex, "\n\n", "User saved sets: ", str(user.saved.snapshots), sep="")
    })

    observe({
        if (!is.null(input$inputs_snapshot) && length(input$inputs_snapshot) > 0) {
      print(input$inputs_snapshot)
            user.saved.snapshots[[length(user.saved.snapshots) + 1]] <<- input$inputs_snapshot
      save(user.saved.snapshots, file="snapshots.Rdata")
        }
    })

  output$input_container <- renderRestoration({
    query <- parseQueryString(session$clientData$url_search)
    if (is.null(query$snapshot)) return (list())
    sid <- as.numeric(query$snapshot)
    if (sid <= length(user.saved.snapshots)) {
      user.saved.snapshots[[sid]]
    }
  })

  output$gen_url <- renderPrint({
    if (length(input$inputs_snapshot) > 0) {
      paste("The current input snapshot is created, and can be restored by visiting: \n",
            session$clientData$url_protocol, "://",
            session$clientData$url_hostname, ":",
            session$clientData$url_port, 
            session$clientData$url_pathname, "?snapshot=", length(user.saved.snapshots),
            sep=""
        )
    }
  })
})

www/js/parse_input.js

$(document).ready(function() {

    if (window.location.search) {
        /* METHOD 1: restore from a explicit URL specifying all inputs */

        var input_params = {};
        /* process query string, e.g. ?obs=10&foo=bar */
        var params = $.map(
            window.location.search.match(/[\&\?]\w+=[^\&]+/g), 
            function(p, i) { 
                var kv = p.substring(1).split("=");
                input_params[kv[0]] = decodeURIComponent(kv[1]);
            }
        );

        // you can uncomment this if you want to restore inputs from an
        // explicit options specified in the URL in format:
        //      input_id=value

        //restore_snapshot("#input_container", input_params);
    }

    var restore_snapshot = function(el, input_params) {
        /* Shiny.inputBindings.getBindings() return the InputBinding instances
           for every (native) input type that Shiny supports (selectInput, textInput,
           actionButton etc.)  */
        $.each(Shiny.inputBindings.getBindings(), function(i, b) {
            /* find all inputs within a specific input type */
            var inputs = b.binding.find(el);
            $.each(inputs, function(j, inp) {
                /* check if the input's id matches the key specified in the query
                   string */
                var inp_val = input_params[$(inp).attr("id")];
                if (inp_val != undefined) {
                    b.binding.setValue(inp, inp_val);
                }
            });
        });
    }

    $("#save_options").on('click', function() {
        /* dump all inputs within input container */
        var input_params = {}
        $.each(Shiny.inputBindings.getBindings(), function(i, b) {
            /* find all inputs within a specific input type */
            var inputs = b.binding.find('#input_container');
            $.each(inputs, function(j, inp) {
                /* check if the input's id matches the key specified in the query
                   string */
                var inp_id = $(inp).attr("id");
                if (inp_id) {
                    input_params[inp_id] = b.binding.getValue(inp);
                }
            });
        });

        console.log(input_params);
        $("#inputs_snapshot").val(JSON.stringify(input_params))
            .trigger("change");
    });

    /* ------------ Shiny Bindings -------------- */
    /* First, an input binding monitor change of a hidden input, 
     * whose value will be changed once the user clicks the 
     * "save current options" button. 
     */
    var snapshotBinding = new Shiny.InputBinding();
    $.extend(snapshotBinding, {
        find: function(scope) {
            return $(scope).find("#inputs_snapshot");
        },
        getValue: function(el) {
            return JSON.parse($(el).val());
        },
        subscribe: function(el, callback) {
            $(el).on("change.snapshot", function(e) {
                callback();
            });
        },
        unsubscribe: function(el) {
            $(el).off(".snapshot");
        }
    });

    Shiny.inputBindings.register(snapshotBinding);

    var restoreBinding = new Shiny.OutputBinding();
    $.extend(restoreBinding, {
        find: function(scope) {
            return $(scope).find("#input_container");
        },
        renderValue: function(el, data) {
            // very rudimentary sanity check
            if ($.isPlainObject(data) && data.hasOwnProperty('username')) {
                restore_snapshot(el, data);
                alert("Snapshot restored!");
            }
        }
    });

    Shiny.outputBindings.register(restoreBinding, 'inputs.Restore');


});

A short explanation:

  • We create two customized input and output binding:
    • The input binding is triggered once the user click the "Save" button, which changes a hidden <input> tag. This allows us to send the current snapshot of inputs to the server.
    • The server uses an observer to watch the snapshot input. It then updates the user.saved.snapshots variable, and save it to a disk file.
    • We also created a customized output binding. The server will use this output binding to send a specific snapshot of user inputs to the client. The server will only send valid data to the client if the query string ?snapshot=[number] is visible.
  • Alternatively, you can use the input$inputs_snapshot list object to create an explicit restoration URL, (e.g. ?username=Eric&age=44&sex=Male), because you can access all input values from there. And our javascript provides that functionality as well.

There are many details need to be polished. You probably can consider save these profiles to a SQLite database using RSQLite package.

But above demo should serve as a good proof of concept.

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