Arrays · mbostock/d3 Wiki. Wiki ▸ API Reference ▸ Core ▸ Arrays 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. JavaScript includes mutator methods that modify the array: There are also accessor methods that return some representation of the array: And finally, iteration methods that apply functions to elements in the array: Ordering # d3.ascending(a, b) Returns -1 if a is less than b, or 1 if a is greater than b, or 0. . # d3.descending(a, b) Returns -1 if a is greater than b, or 1 if a is less than b, or 0. . # d3.min(array[, accessor]) Find max from any of three arrays. Array. The JavaScript Array class is a global object that is used in the construction of arrays; which are high-level, list-like objects. Description Arrays are list-like objects whose prototype has methods to perform traversal and mutation operations.
Neither the length of a JavaScript array nor the types of its elements are fixed. Since an array's length can change at any time, and data can be stored at non-contiguous locations in the array, JavaScript arrays are not guaranteed to be dense; this depends on how the programmer chooses to use them. Arrays cannot use strings as element indexes (as in an associative array) but must use integers. Common operations Create an Array let fruits = ['Apple', 'Banana'] console.log(fruits.length) Access an Array item using the index position let first = fruits[0] let last = fruits[fruits.length - 1] Loop over an Array fruits.forEach(function(item, index, array) { console.log(item, index)}) Add an item to the end of an Array let newLength = fruits.push('Orange')
D3, Conceptually - Lesson 3: (Moderately) Advanced Data. So, shall we blow your mind? Maybe? Maybe it isn't actually that impressive. Maybe I should just go home and stop writing... or not. I've really got nothing better to do, honestly. So. The easiest one to explain is the data call. The harder part is the line before that – the selectAll called on an existing multi-element selection. <div class='outer'><div class='inner'></div><div class='inner'></div></div><div class='outer'><div class='inner'></div><div class='inner'></div><div class='inner'></div></div>var outerDivs = d3.selectAll('div.outer'); outerDivs.insert('div', '.inner') .text(function(d, outerIndex) { return 'I\'m outer div number ' + outerIndex + '!
' The insert method used in the example is new. The example is either a surprise to you, dear reader, or completely expected behavior. Yes, yes, back to the matter at hand—in the example, the line d3.selectAll('div.outer') results in a selection that, conceptually, looks like this: Or, in more detail: Underscore’s Equivalents in D3. Collections each(array) Underscore example: _.each([1, 2, 3], function(num) { alert(num); }); Vanilla equivalent: [1, 2, 3].forEach(function(num) { alert(num); }); each(object) D3 equivalent using d3.values (d3.entries and d3.map forEach would also work): map(array) _.map([1, 2, 3], function(num) { return num * 3; }); [1, 2, 3].map(function(num) { return num * 3; }); map(object) D3 equivalent with d3.values (d3.entries and d3.map values.map would also work): reduce var sum = _.reduce([1, 2, 3], function(memo, num) { return memo + num; }, 0); var sum = [1, 2, 3].reduce(function(memo, num) { return memo + num; }, 0); reduceRight Given: var list = [[0, 1], [2, 3], [4, 5]]; var flat = _.reduceRight(list, function(a, b) { return a.concat(b); }, []); var flat = list.reduceRight(function(a, b) { return a.concat(b); }, []); find var even = _.find([1, 2, 3, 4, 5, 6], function(num) { return num % 2 == 0; }); var even = [1, 2, 3, 4, 5, 6].filter(function(num) { return num % 2 == 0; })[0]; contains invoke pluck max min sortBy.
TheCodingTutorials: D3. In my previous tutorial, I showed how to import data from a CSV file or a text file. However, oftentimes the type of data that you need to use has multiple columns, like so: Column 1 Title, Column 2 Title, Column 3 Title 1, 2, 3 4, 5, 6 rather than being in a single column format, like this: One common reason for having multi-column data is if all of the data can be split into categories and you need to visually show which category each piece of data is in, through colors, spacing, positioning, highlighting, font size, or etc. In this tutorial, I'm just going to show you how to fully reconstruct the data by accessing it in memory, as it's not entirely the simplest thing for a beginner to do. D3 nest examples. Here is my learning process for getting to grips with nest.
Discovered the d3 tests half way through which were a great help: tests Simple one level nest In Bl.ocks.org, click on "Open in a New Window" (bottom right) to view all the examples Group by status var nested_data = d3.nest() .key(function(d) { return d.status; }) .entries(csv_data); Simple two level nest Group by status then priority var nested_data = d3.nest() .key(function(d) { return d.status; }) .key(function(d) { return d.priority; }) .entries(csv_data); Use rollup to count leaves The leaf level is replaced by a value at the parent level var nested_data = d3.nest() .key(function(d) { return d.status; }) .key(function(d) { return d.priority; }) .rollup(function(leaves) { return leaves.length; }) .entries(csv_data); Rollup does sums as well Can't have two rollups, but can return an object/array Rollup everything to get a grand total of number of lines No key Sorting Each level can be sorted by key - a simple ascending or descending...
D3.js Tips and Tricks: Grouping and summing data using d3.nest.