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Choices/selected settings

Source: R/picks.R
picks.Rd

Define choices and default selection for variables. picks allows app-developer to specify datasets, variables and values to be selected by app-user during Shiny session. Functions are based on the idea of choices/selected where app-developer provides choices and what is selected by default. App-user changes selected interactively (see picks_module).

Usage 

picks(..., check_dataset = TRUE)

datasets(choices = tidyselect::everything(), selected = 1L, fixed = NULL, ...)

variables(
  choices = tidyselect::everything(),
  selected = 1L,
  multiple = NULL,
  fixed = NULL,
  ordered = FALSE,
  ...
)

values(
  choices = function(x) !is.na(x),
  selected = function(x) !is.na(x),
  multiple = TRUE,
  fixed = NULL,
  ...
)

Arguments

...

for picks(...): hierarchical structure that contains datasets() as first element and optionally variables() and values()

for variables(...) and values(...): additional arguments delivered to pickerInput

check_dataset

(logical(1)) whether to check that the first element of picks is datasets(). This is useful to set to FALSE when creating picks objects that have a required dataset that is not selected by the user and defined in the module itself.

choices

(tidyselect::language or character) Available values to choose.

selected

(tidyselect::language or character) Choices to be selected.

fixed

(logical(1)) selection will be fixed and not possible to change interactively.

multiple

(logical(1)) if more than one selection is possible.

ordered

(logical(1)) if the selected should follow the selection order. If FALSE selected returned from srv_module_input() would be ordered according to order in choices.

Value

For picks() it returns an object of picks class, which is a list of pick objects with additional attributes for Shiny interactivity. For datasets(), variables(), and values() it returns a pick object with class corresponding to the type of selection including the choices and selected values.

tidyselect support

Both choices and selected parameters support tidyselect syntax, enabling dynamic and flexible variable selection patterns. This allows choices to be determined at runtime based on data characteristics rather than hard-coded values.

Using tidyselect for choices and selected

When choices uses tidyselect, the available options are determined dynamically based on actually selected data:

  • tidyselect::everything() - All variables/datasets

  • tidyselect::starts_with("prefix") - Variables starting with a prefix

  • tidyselect::ends_with("suffix") - Variables ending with a suffix

  • tidyselect::contains("pattern") - Variables containing a pattern

  • tidyselect::matches("regex") - Variables matching a regular expression

  • tidyselect::where(predicate) - Variables/datasets satisfying a predicate function

  • tidyselect::all_of(vars) - All specified variables (error if missing)

  • tidyselect::any_of(vars) - Any specified variables (silent if missing)

  • Range selectors like Sepal.Length:Petal.Width - Variables between two positions

  • Integer indices (e.g., 1L, 1L:3L, c(1L, 3L, 5L)) - Select by position. Be careful, must be integer!

The selected parameter can use the same syntax but it will be applied to the subset defined in choices. This means that choices = is.numeric, selected = is.factor or choices = c("a", "b", "c"), selected = c("d", "e") will imply en empty selected.

Warning: Using explicit character values for selected with dynamic choices may cause issues if the selected values are not present in the dynamically determined choices. Prefer using numeric indices (e.g., 1 for first variable) when choices is dynamic.

Structure and element dependencies

The picks() function creates a hierarchical structure where elements depend on their predecessors, enabling cascading reactive updates during Shiny sessions.

Element hierarchy

A picks object must follow this order:

  1. datasets() - to select a dataset. Always the first element (required).

  2. variables() - To select columns from the chosen dataset.

  3. values() - To select specific values from the chosen variable(s).

Each element's choices are evaluated within the context of its predecessor's selection.

How dependencies work

  • Fixed dataset: When datasets(choices = "iris") specifies one dataset, the variables() choices are evaluated against that dataset columns.

  • Multiple dataset choices: When datasets(choices = c("iris", "mtcars")) allows multiple options, variables() choices are re-evaluated each time the user selects a different dataset. This creates a reactive dependency where variable choices update automatically.

  • Dynamic dataset choices: When using datasets(choices = tidyselect::where(is.data.frame)), all available data frames are discovered at runtime, and variable choices adapt to whichever dataset the user selects.

  • Variable to values: Similarly, values() choices are evaluated based on the selected variable(s), allowing users to filter specific levels or values. When multiple variables are selected, then values will be a concatenation of the columns.

Best practices

  • Always start with datasets() - this is enforced by validation

  • Use dynamic choices in variables() when working with multiple datasets to ensure compatibility across different data structures

  • Prefer tidyselect::everything() or tidyselect::where() predicates for flexible variable selection that works across datasets with different schemas

  • Use numeric indices for selected when choices are dynamic to avoid referencing variables that may not exist in all datasets

Important: values() requires type-aware configuration

Why values() is different from datasets() and variables()

datasets() and variables() operate on named lists of objects, meaning they work with character-based identifiers. This allows you to use text-based selectors like starts_with("S") or contains("prefix") consistently for both datasets and variable names.

values() is fundamentally different because it operates on the actual data content within a selected variable (column). The type of data in the column determines what kind of filtering makes sense:

  • numeric columns (e.g., age, height, price) contain numbers

  • character/factor columns (e.g., country, category, status) contain categorical values

  • Date/POSIXct columns contain temporal data

  • logical columns contain TRUE/FALSE values

Type-specific UI controls

The values() function automatically renders different UI controls based on data type:

  • numeric data: Creates a sliderInput for range selection

    • choices must be a numeric vector of length 2: c(min, max)

    • selected must be a numeric vector of length 2: c(selected_min, selected_max)

  • Categorical data (character/factor): Creates a pickerInput for discrete selection

    • choices can be a character vector or predicate function

    • selected can be specific values or a predicate function

  • Date/POSIXct data: Creates date/datetime range selectors

    • choices must be a Date or POSIXct vector of length 2

  • logical data: Creates a checkbox or picker for TRUE/FALSE selection

Developer responsibility

App developers must ensure values() configuration matches the variable type:

  1. Know your data: Understand what type of variable(s) users might select

  2. Configure appropriately: Set choices and selected to match expected data types

  3. Use predicates for flexibility: When variable type is dynamic, use predicate functions like function(x) !is.na(x) (the default) to handle multiple types safely

Examples of correct usage 

# For a numeric variable (e.g., age)
picks(
  datasets(choices = "demographic"),
  variables(choices = "age", multiple = FALSE),
  values(choices = c(0, 100), selected = c(18, 65))
)

# For a categorical variable (e.g., country)
picks(
  datasets(choices = "demographic"),
  variables(choices = "country", multiple = FALSE),
  values(choices = c("USA", "Canada", "Mexico"), selected = "USA")
)

# Safe approach when variable type is unknown - use predicates
picks(
  datasets(choices = "demographic"),
  variables(choices = tidyselect::everything(), selected = 1L),
  values(choices = function(x) !is.na(x), selected = function(x) !is.na(x))
)

Common mistakes to avoid 

# WRONG: Using string selectors for numeric data
values(choices = starts_with("5"))  # Doesn't make sense for numeric data!

# WRONG: Providing categorical choices for a numeric variable
values(choices = c("low", "medium", "high"))  # Won't work if variable is numeric!

# WRONG: Providing numeric range for categorical variable
values(choices = c(0, 100))  # Won't work if variable is factor/character!

Example: Three-level hierarchy 

picks(
  datasets(choices = c("iris", "mtcars"), selected = "iris"),
  variables(choices = tidyselect::where(is.numeric), selected = 1L),
  values(choices = tidyselect::everything(), selected = seq_len(10))
)

In this example:

  • User first selects a dataset (iris or mtcars)

  • Variable choices update to show only numeric columns from selected dataset

  • After selecting a variable, value choices show all unique values from that column

Examples 

# Select columns from iris dataset using range selector
picks(
  datasets(choices = "iris"),
  variables(choices = Sepal.Length:Petal.Width, selected = 1L)
)
#>  <picks>
#>    <datasets>:
#>      choices: iris
#>      selected: 1L
#>      multiple=FALSE, ordered=FALSE, fixed=TRUE
#>    <variables>:
#>      choices: Sepal.Length:Petal.Width
#>      selected: 1L
#>      multiple=FALSE, ordered=FALSE, fixed=FALSE, allow-clear=FALSE

# Single variable selection from iris dataset
picks(
  datasets(choices = "iris", selected = "iris"),
  variables(choices = c("Sepal.Length", "Sepal.Width"), selected = "Sepal.Length", multiple = FALSE)
)
#>  <picks>
#>    <datasets>:
#>      choices: iris
#>      selected: iris
#>      multiple=FALSE, ordered=FALSE, fixed=TRUE
#>    <variables>:
#>      choices: Sepal.Length, Sepal.Width
#>      selected: Sepal.Length
#>      multiple=FALSE, ordered=FALSE, fixed=FALSE, allow-clear=FALSE

# Dynamic selection: any variable from iris, first selected by default
picks(
  datasets(choices = "iris", selected = "iris"),
  variables(choices = tidyselect::everything(), selected = 1L, multiple = FALSE)
)
#>  <picks>
#>    <datasets>:
#>      choices: iris
#>      selected: iris
#>      multiple=FALSE, ordered=FALSE, fixed=TRUE
#>    <variables>:
#>      choices: tidyselect::everything()
#>      selected: 1L
#>      multiple=FALSE, ordered=FALSE, fixed=FALSE, allow-clear=FALSE

# Multiple dataset choices: variable choices will update when dataset changes
picks(
  datasets(choices = c("iris", "mtcars"), selected = "iris"),
  variables(choices = tidyselect::everything(), selected = 1L, multiple = FALSE)
)
#>  <picks>
#>    <datasets>:
#>      choices: iris, mtcars
#>      selected: iris
#>      multiple=FALSE, ordered=FALSE, fixed=FALSE
#>    <variables>:
#>      choices: tidyselect::everything()
#>      selected: 1L
#>      multiple=FALSE, ordered=FALSE, fixed=FALSE, allow-clear=FALSE

# Select from any dataset, filter by numeric variables
picks(
  datasets(choices = c("iris", "mtcars"), selected = 1L),
  variables(choices = tidyselect::where(is.numeric), selected = 1L)
)
#>  <picks>
#>    <datasets>:
#>      choices: iris, mtcars
#>      selected: 1L
#>      multiple=FALSE, ordered=FALSE, fixed=FALSE
#>    <variables>:
#>      choices: <fn>
#>      selected: 1L
#>      multiple=FALSE, ordered=FALSE, fixed=FALSE, allow-clear=FALSE

# Fully dynamic: auto-discover datasets and variables
picks(
  datasets(choices = tidyselect::where(is.data.frame), selected = 1L),
  variables(choices = tidyselect::everything(), selected = 1L, multiple = FALSE)
)
#>  <picks>
#>    <datasets>:
#>      choices: <fn>
#>      selected: 1L
#>      multiple=FALSE, ordered=FALSE, fixed=FALSE
#>    <variables>:
#>      choices: tidyselect::everything()
#>      selected: 1L
#>      multiple=FALSE, ordered=FALSE, fixed=FALSE, allow-clear=FALSE

# Select categorical variables with length constraints
picks(
  datasets(choices = tidyselect::everything(), selected = 1L),
  variables(choices = is_categorical(min.len = 2, max.len = 15), selected = seq_len(2))
)
#>  <picks>
#>    <datasets>:
#>      choices: tidyselect::everything()
#>      selected: 1L
#>      multiple=FALSE, ordered=FALSE, fixed=FALSE
#>    <variables>:
#>      choices: <fn>
#>      selected: <int>
#>      multiple=FALSE, ordered=FALSE, fixed=FALSE, allow-clear=FALSE