What is the difference D3 datum vs. data?

Question

Can someone please explain the difference between datum() and data() in D3.js? I see both being used and I am not sure why you should choose one over the other?

Answer 1

Here are some good links:

• Good discussion on D3 "data()": Understanding how D3.js binds data to nodes

• D3 for Mere Mortals

• Mike Bostock's D3 Wiki

Per the latter:

# selection.data([values[, key]])

Joins the specified array of data with the current selection. The specified values is an array of data values, such as an array of numbers or objects, or a function that returns an array of values.

...

# selection.datum([value])

Gets or sets the bound data for each selected element. Unlike the selection.data method, this method does not compute a join (and thus does not compute enter and exit selections).