reactives

Keyed collections of shiny reactives whose keys can be added, removed and reordered, with dependencies tracked per key.

Shiny’s reactive building blocks leave a gap:

	A single one	A keyed collection	In this package
Stored	reactiveVal()	reactiveValues()	reactive_vals()
Computed	reactive()	none	reactive_exprs()

A reactiveValues() object can gain keys, but it can’t remove or reorder them (rstudio/shiny#2439), and shiny has no keyed collection of computed values. This package fills both gaps with collections whose keys can be added, removed and reordered: reactive_vals() for stored values, reactive_exprs() for computed ones, and reactives() for both kinds at once.

Background

The package grows out of two workarounds in blockr.core. One is trim_rv(), which removes keys from a reactiveValues() object through shiny’s internals. The other is the reactives class, which holds the computed inputs of variadic blocks.

Usage

library(shiny)
library(reactives)

# Let reactives be read at the console, as inside an app
reactiveConsole(TRUE)

x <- reactives(a = reactiveVal(1), b = reactive(2 * 21))

# Reading with `$` or `[[` returns a slot's value, as on reactiveValues()
x$a
#> [1] 1
x[["b"]]
#> [1] 42

# A slot that doesn't exist reads as NULL, as on a list
is.null(x$c)
#> [1] TRUE

# Assigning a value writes it to the slot, adding the slot if there is none
x$a <- 10
x$c <- "new"

# With `[`, a slot's reactive is read, bound or removed
is.reactive(x["a"])
#> [1] TRUE
x["d"] <- reactive(x$a + 1)
x["b"] <- NULL
names(x)
#> [1] "a" "c" "d"

Inside an observer or a reactive(), reading a slot creates a dependency on that slot alone, and reading its value with $ or [[ one on the value as well. The reader re-runs when that slot is added, replaced or removed, or when the value it read changes, but not when other slots change.

Status

Under development. Planned work is tracked in the issues.

Installation

# install.packages("pak")
pak::pak("nbenn/reactives")