Accessing Question Values

In surveydown, you often need to access the values that respondents have entered in your survey questions. This is essential for implementing conditional logic, creating reactive content, performing calculations, or storing derived values.

The primary way to access question values in your app.R file is through the sd_value() and sd_values() functions. The two functions are aliases - they work identically, so use whatever name is easier to remember for you. For the documentation, we’ll just be using sd_value().

Basic Usage

The sd_value() function retrieves the value(s) that a respondent has entered for one or more questions.

Single Question Value

To get the value of a single question, pass the question ID to sd_value():

server <- function(input, output, session) {

  # Get the value of a single question
  fruit_choice <- sd_value("fruit")

  sd_server()
}

Multiple Question Values

You can retrieve multiple question values at once by passing multiple question IDs. This returns a vector of values:

server <- function(input, output, session) {

  # Get values from multiple questions
  food_choices <- sd_value("fruit", "vegetable", "protein")
  # Returns the vector of chosen values, something like c("apple", "lettuce", "chicken")

  sd_server()
}

Quoted vs Unquoted IDs

One of the convenient features of sd_value() is that it accepts both quoted and unquoted question IDs:

# Both of these work identically:
sd_value("fruit")
sd_value(fruit)

# Also works with multiple IDs:
sd_value("fruit", "vegetable")
sd_value(fruit, vegetable)

Choose whichever style you prefer - they function the same way.

Automatic Type Detection

One of the most convenient features of sd_value() is its automatic type detection and conversion. By default, the function intelligently determines the appropriate data type and format for the returned value.

Automatic Numeric Conversion

When sd_value() retrieves a value that looks numeric, it automatically converts it to a numeric type. This means you don’t need to manually call as.numeric():

# If age question value is "25", sd_value() returns 25 (numeric)
age <- sd_value("age")

# You can use it directly in numeric operations
if (age > 18) {
  # Do something
}

# Works in calculations too
age_in_months <- sd_value("age") * 12

If a value cannot be converted to numeric (e.g., it contains letters), sd_value() returns it as a character string.

Automatic Vector Splitting

For multiple-choice questions that allow multiple selections (like mc_multiple), responses are often stored with pipe separators (e.g., "apple|banana|orange"). The sd_value() function automatically detects and splits these into a vector:

# If the stored value is "apple|banana|orange"
fruits <- sd_value("favorite_fruits")
# Returns: c("apple", "banana", "orange")

# You can use it directly in vector operations
if ("apple" %in% fruits) {
  # Do something
}

Controlling Type Conversion

While automatic detection works well in most cases, you can override this behavior using the as_numeric and as_vector parameters:

Force numeric conversion:

# Always convert to numeric (non-convertible values become NA)
val <- sd_value("some_field", as_numeric = TRUE)

Prevent numeric conversion:

This is useful for values like ZIP codes that should stay as strings to preserve leading zeros:

# Keep as string (e.g., "01234" stays "01234", not converted to 1234)
zip <- sd_value("zip_code", as_numeric = FALSE)

ZIP Code Special Case

ZIP codes require as_numeric = FALSE to preserve leading zeros. Without it, automatic conversion will strip the leading zero:

# Without as_numeric = FALSE (WRONG for ZIP codes):
zip <- sd_value("zip")
# "01234" becomes 1234 - leading zero lost!

# With as_numeric = FALSE (CORRECT for ZIP codes):
zip <- sd_value("zip", as_numeric = FALSE)
# "01234" stays as "01234" - preserved correctly

This matters when you need to check the length:

# Validate ZIP code length - must use as_numeric = FALSE
sd_stop_if(
  nchar(sd_value("zip", as_numeric = FALSE)) != 5 ~ "ZIP code must be 5 digits."
)

Without as_numeric = FALSE, the ZIP code "01234" would be converted to 1234, and nchar(1234) would return 4, incorrectly rejecting a valid ZIP code.

Force vector splitting:

# Always split on pipe, even if no pipe is present
vals <- sd_value("some_field", as_vector = TRUE)

Prevent vector splitting:

# Keep as single string, don't split
raw <- sd_value("favorite_fruits", as_vector = FALSE)
# Returns: "apple|banana|orange" (as single string)

Key Features

Reactive by Default

sd_value() is a reactive function, which means it automatically updates whenever the question value changes. This makes it ideal for use in reactive contexts like observe(), reactive(), or within sd_show_if() conditions.

Important: Because sd_value() is reactive, it can only be used inside the server() function in your app.R file, not in the survey.qmd file.

Persistence After Refresh

When cookies are enabled (the default), sd_value() will restore user inputs from the database even after a page refresh. This ensures that respondents don’t lose their progress if they accidentally refresh the page or close and reopen the survey.

Replacement for `input$`

If you’re familiar with Shiny, you might know about accessing inputs using input$question_id. In surveydown, you should use sd_value() instead of input$ because:

sd_value() restores values after page refresh
sd_value() provides cleaner syntax with support for unquoted IDs
sd_value() works seamlessly with surveydown’s data persistence features

Common Use Cases

Conditional Logic

Use sd_value() to check question responses and show/hide content:

server <- function(input, output, session) {

  sd_show_if(
    sd_value("pet_type") == "dog" ~ "dog_breed",
    sd_value("pet_type") == "cat" ~ "cat_breed"
  )

  sd_server()
}

See the Conditional Logic page for more details.

Numeric Calculations

When working with numeric questions, sd_value() automatically converts values to numbers, so you can use them directly in calculations:

server <- function(input, output, session) {

  # Create a reactive calculation
  # sd_value() automatically converts to numeric
  total <- reactive({
    sd_value("price") * sd_value("quantity")
  })

  # Store the calculated value
  sd_reactive("total_cost", total())

  sd_server()
}

Checking Multiple Choice Selections

For mc_multiple or mc_multiple_buttons questions that return vectors:

server <- function(input, output, session) {

  # Check if a specific option was selected
  sd_show_if(
    "apple" %in% sd_value("favorite_fruits") ~ "apple_question"
  )

  # Check how many options were selected
  sd_show_if(
    length(sd_value("favorite_fruits")) >= 3 ~ "fruit_lover"
  )

  sd_server()
}

Creating Derived Values

You can use question values to create new values and store them:

server <- function(input, output, session) {

  # Create a derived value based on responses
  # sd_value() automatically converts age to numeric
  category <- reactive({
    age <- sd_value("age")
    if (age < 18) {
      "minor"
    } else if (age < 65) {
      "adult"
    } else {
      "senior"
    }
  })

  # Store the category for later analysis
  sd_store_value(category = category())

  sd_server()
}

Checking if Questions are Answered

Use sd_is_answered() to check if a question has been answered at all:

server <- function(input, output, session) {

  sd_show_if(
    sd_is_answered("name") ~ "greeting_message"
  )

  sd_server()
}

This is especially useful when you want to show follow-up content once any answer is provided, regardless of which specific option was chosen.

Important Notes

NULL Values

If a question hasn’t been answered yet, sd_value() returns NULL. Always check for this when performing operations that might fail on NULL:

# Safe approach for conditional logic
age <- sd_value("age")
if (!is.null(age) && age > 18) {
  # Do something
}

Matrix Questions

For matrix type questions, sd_is_answered() only returns TRUE if all sub-questions (rows) have been answered.

Automatic Type Detection

Thanks to automatic type detection, sd_value() handles data type conversion for you:

# Numeric values are automatically converted
# This works directly, no need for as.numeric()
if (sd_value("age") > 18) {
  # This works because sd_value() returns 25 (numeric), not "25" (string)
}

# Pipe-separated values are automatically split into vectors
# This works directly, no need to split manually
if ("apple" %in% sd_value("favorite_fruits")) {
  # This works because sd_value() returns c("apple", "banana"), not "apple|banana"
}

The only time you need to manually control type conversion is for special cases like ZIP codes with leading zeros. In those cases, use as_numeric = FALSE to prevent conversion (see Controlling Type Conversion above).

Basic Usage

Single Question Value

Multiple Question Values

Quoted vs Unquoted IDs

Automatic Type Detection

Automatic Numeric Conversion

Automatic Vector Splitting

Controlling Type Conversion

Key Features

Reactive by Default

Persistence After Refresh

Replacement for input$

Common Use Cases

Conditional Logic

Numeric Calculations

Checking Multiple Choice Selections

Creating Derived Values

Checking if Questions are Answered

Important Notes

NULL Values

Matrix Questions

Automatic Type Detection

Related Functions

Replacement for `input$`