knitr::opts_chunk$set(eval = FALSE)
R objects provided as data
for D3 visualizations are converted to JSON using the jsonlite::toJSON() function, and use the same default serialization behavior as Shiny and htmlwidgets.
This corresponds to the following call to jsonlite::toJSON()
:
jsonlite::toJSON( dataframe = "columns", null = "null", na = "null", auto_unbox = TRUE, digits = getOption("shiny.json.digits", 16), use_signif = TRUE, force = TRUE, POSIXt = "ISO8601", UTC = TRUE, rownames = FALSE, keep_vec_names = TRUE, json_verabitm = TRUE )
Data frames are serialized with a columns orientation as that is a more compact over the wire representation than rows orientation. When the data frame gets to the client r2d3 calls the HTMLWidgets.dataframeToD3() method to transform the data to a D3-friendly rows orientation.
Here is an example of the JSON columns-based representation of an R data frame:
{ "Sepal.Length": [5.1, 4.9, 4.7], "Sepal.Width": [3.5, 3, 3.2], "Petal.Length": [1.4, 1.4, 1.3], "Petal.Width": [0.2, 0.2, 0.2], "Species": ["setosa", "setosa", "setosa"] }
After we apply HTMLWidgets.dataframeToD3()
, it will become:
[ { "Sepal.Length": 5.1, "Sepal.Width": 3.5, "Petal.Length": 1.4, "Petal.Width": 0.2, "Species": "setosa" }, { "Sepal.Length": 4.9, "Sepal.Width": 3, "Petal.Length": 1.4, "Petal.Width": 0.2, "Species": "setosa" }, { "Sepal.Length": 4.7, "Sepal.Width": 3.2, "Petal.Length": 1.3, "Petal.Width": 0.2, "Species": "setosa" } ]
If you don't like the default JSON conversion provided for data
, you can write your own function that uses jsonlite to perform a custom conversion. For example:
data_to_json <- function(data) { jsonlite::toJSON(data, dataframe = "rows", auto_unbox = FALSE, rownames = TRUE) } r2d3(data = data_to_json(x), script = "barchart.js")
When a value returned from jsonlite::toJSON()
is passed as the data
argument r2d3 won't attempt any additional conversion or transformation of the value.
You can implement the as_d3_data()
S3 method to provide custom converters for any R class. For example, you could create an S3 method for the igraph
class to convert data into a JSON that is optimized for rendering by a D3 network visualization:
as_d3_data.igraph <- function(x, ...) { # code to serialize igraph to D3 network friendly JSON }
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