local_image: Helper function for adding a local image

Description

We can flexibly add a local image (i.e., an image residing on disk) inside of a table with local_image() function. The function provides a convenient way to generate an HTML fragment using an on-disk PNG or SVG. Because this function is currently HTML-based, it is only useful for HTML table output. To use this function inside of data cells, it is recommended that the text_transform() function is used. With that function, we can specify which data cells to target and then include a local_image() call within the required user-defined function (for the fn argument). If we want to include an image in other places (e.g., in the header, within footnote text, etc.) we need to use local_image() within the html() helper function.

Usage

local_image(filename, height = 30)

Value

A character object with an HTML fragment that can be placed inside of a cell.

Arguments

filename: A path to an image file.
height: The absolute height (px) of the image in the table cell.

Examples

Create a tibble that contains heights of an image in pixels (one column as a string, the other as numerical values), then, create a gt table. Use the text_transform() function to insert a local test image (PNG) image with the various sizes.

dplyr::tibble(
  pixels = px(seq(10, 35, 5)),
  image = seq(10, 35, 5)
) %>%
  gt() %>%
  text_transform(
    locations = cells_body(columns = image),
    fn = function(x) {
      local_image(
        filename = test_image(type = "png"),
        height = as.numeric(x)
      )
    }
  )

This image of a table was generated from the first code example in the `local_image()` help file.

Function ID

8-2

Details

By itself, the function creates an HTML image tag with an image URI embedded within. We can easily experiment with a local PNG or SVG image that's available in the gt package using the test_image() function. Using that, the call local_image(file = test_image(type = "png")) evaluates to:

<img src=<data URI> style=\"height:30px;\">

where a height of 30px is a default height chosen to work well within the heights of most table rows.