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The **intrval** R package is lightweight (~11K), standalone (apart from importing from **graphics**, has exactly 0 non-**base** dependency), and it has a very narrow scope: it implements relational operators for intervals — very well aligned with the *tiny manifesto*. In this post we will explore the use of the package in two **shiny** apps with sliders.

The first example uses a regular slider that returns a single value. To make that an interval, we will use standard deviation (SD, *sigma*) in a quality control chart (QCC). The code is based on the `pistonrings`

data set from the **qcc** package. The Shewhart chart sets 3-_sigma_ limit to indicate state of control. The slider is used to adjusts the *sigma* limit and the GIF below plays is as an animation.

```
library(shiny)
library(intrval)
library(qcc)
data(pistonrings)
mu <- mean(pistonrings$diameter[pistonrings$trial])
SD <- sd(pistonrings$diameter[pistonrings$trial])
x <- pistonrings$diameter[!pistonrings$trial]
## UI function
ui <- fluidPage(
plotOutput("plot"),
sliderInput("x", "x SD:",
min=0, max=5, value=0, step=0.1,
animate=animationOptions(100)
)
)
# Server logic
server <- function(input, output) {
output$plot <- renderPlot({
Main <- paste("Shewhart quality control chart",
"diameter of piston rings", sprintf("+/- %.1f SD", input$x),
sep="\n")
iv <- mu + input$x * c(-SD, SD)
plot(x, pch = 19, col = x %)(% iv +1, type = "b",
ylim = mu + 5 * c(-SD, SD), main = Main)
abline(h = mu)
abline(h = iv, lty = 2)
})
}
## Run shiny app
if (interactive()) shinyApp(ui, server)
```

The second example uses range slider returning two values, which is our interval. To spice things up a bit, we combine intervals on two axes to color some random points. The next range slider defines a distance interval and colors the random points inside the ring.

```
library(shiny)
library(intrval)
set.seed(1)
n <- 10^4
x <- round(runif(n, -2, 2), 2)
y <- round(runif(n, -2, 2), 2)
d <- round(sqrt(x^2 + y^2), 2)
## UI function
ui <- fluidPage(
titlePanel("intrval example with shiny"),
sidebarLayout(
sidebarPanel(
sliderInput("bb_x", "x value:",
min=min(x), max=max(x), value=range(x),
step=round(diff(range(x))/20, 1), animate=TRUE
),
sliderInput("bb_y", "y value:",
min = min(y), max = max(y), value = range(y),
step=round(diff(range(y))/20, 1), animate=TRUE
),
sliderInput("bb_d", "radial distance:",
min = 0, max = max(d), value = c(0, max(d)/2),
step=round(max(d)/20, 1), animate=TRUE
)
),
mainPanel(
plotOutput("plot")
)
)
)
# Server logic
server <- function(input, output) {
output$plot <- renderPlot({
iv1 <- x %[]% input$bb_x & y %[]% input$bb_y
iv2 <- x %[]% input$bb_y & y %[]% input$bb_x
iv3 <- d %()% input$bb_d
op <- par(mfrow=c(1,2))
plot(x, y, pch = 19, cex = 0.25, col = iv1 + iv2 + 3,
main = "Intersecting bounding boxes")
plot(x, y, pch = 19, cex = 0.25, col = iv3 + 1,
main = "Deck the halls:\ndistance range from center")
par(op)
})
}
## Run shiny app
if (interactive()) shinyApp(ui, server)
```

If you think there are other use cases for **intrval** in **shiny** applications, let me know in the comments section!

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**Peter Solymos - R related posts**.

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