Arrays

API Reference

When using D3—and doing data visualization in general—you tend to do a lot of array manipulation. That's because D3's canonical representation of data is an array. Some common forms of array manipulation include taking a contiguous slice (subset) of an array, filtering an array using a predicate function, and mapping an array to a parallel set of values using a transform function. Before looking at the set of utilities that D3 provides for arrays, you should familiarize yourself with the powerful array methods built-in to JavaScript.

This includes mutator methods that modify the array:

• reverse - Reverse the order of the elements of the array.
• shift - Remove the first element from the array.
• sort - Sort the elements of the array.
• splice - Add or remove elements from the array.
• unshift - Add one or more elements to the front of the array.

There are also accessor methods that return some representation of the array:

• concat - Join the array with other array(s) or value(s).
• join - Join all elements of the array into a string.
• slice - Extract a section of the array.
• indexOf - Find the first occurrence of a value within the array.
• lastIndexOf - Find the last occurrence of a value within the array.

And finally, iteration methods that apply functions to elements in the array:

• filter - Create a new array with only the elements for which a predicate is true.
• forEach - Call a function for each element in the array.
• every - See if every element in the array satisfies a predicate.
• map - Create a new array with the result of a function of every element in the array.
• some - See if at least one element in the array satisfies a predicate.
• reduce - Apply a function to reduce the array to a single value (from left-to-right).
• reduceRight - Apply a function to reduce the array to a single value (from right-to-left).