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# D3-Notes
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# D3.js
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## Basics
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- Selection
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- `d3.select()`
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- like document.querySelector()
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- `d3.selectAll()`
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- like document.querySelectorAll()
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- can make selections from within selections
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-`d3.select('main').selectAll('span');`
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- .style()
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- sets the style for an element
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- `d3.select('div').style('color', 'orange');`
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- can pass an object
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- `d3.select('div').style({'color': 'blue', 'font-size': '40px'});`
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- style will return the selection for chaining
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- `d3.select('div').style('color', 'orange').style({'color': 'blue', 'font-size': '40px'});`
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- .attr()
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- adds/changes an attribute on an selection
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- `d3.select('div').attr('anExampleAttribute', 'someValue');`
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- .classed()
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- checks to see if all elements in selection contain the chosen class
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- `d3.selectAll('.house').classed('house');`
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- returns true
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- `d3.selectAll('div').classed('house');`
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- returns false if not all divs contain class `house`
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- chaining doesn't work since it returns true or false
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- can add the class using
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- `d3.selectAll('div').classed('frog', true);`
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- returns the selection, so you can chain
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- can remove the class using
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- `d3.selectAll('div').classed('frog', false);`
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- .append()
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- append html to a selection
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- returns the appended element
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- `d3.selectAll('div').append('span')`
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- .html()
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- change the inner html of an element
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- .text()
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- set the content of the selection to the exact text (no html)
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## SVG
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- SVG tag is inline
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- Positioning
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- (0,0) - x = 0, y = 0
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- starts at top left
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- y increases vertically down
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- can use negative values
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- -x goes left
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- -y goes up
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- Styling
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- attributes
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- `fill` fill color
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- `stroke` stroke color
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- `stroke-width` width of stroke
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- can also be set inside the `stroke` attribute
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- Group
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- `<g></g>`
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- can put multiple elements inside it.
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- positioning and styling apply to children
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- Circle
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- attributes
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- `r` radius
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- `cx` x position
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- `cy` y position
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```xml
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<svg height="800" width="500">
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<circle/>
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<circle r="50"/>
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<circle r="50" cx="200" cy="300"/>
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</svg>
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```
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- Line
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- attributes
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- `x1` starting x position
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- `y1` starting y position
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- `x2` ending x position
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- `y2` ending y position
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```xml
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<svg height="800" width="500">
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<line/>
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<line x1="0" y1="0" x2="100" y2="100"/> <!-- no stroke, so invisible -->
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<line x1="0" y1="0" x2="100" y2="100" stroke="purple"/>
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<line x1="10" y1="0" x2="10" y2="100" stroke="red"/>
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<line x1="30" y1="10" x2="130" y2="10" stroke="blue"/>
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</svg>
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```
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- Text
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- Content of tag is the text
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- Transform
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- `transform = "translate(x,y)"`
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- `transform = "scale(factor)"`
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- `rotate = "rotate(degrees)"`
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## Request
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- AJAX functions
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- `d3.json('path', function(error, data){});`
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- `d3.csv('path', function(error, data){});`
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- `d3.text('path', function(error, data){});`
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- `d3.html('path', function(error, data){});`
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- `d3.tsv('path', function(error, data){});`
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- `d3.xml('path', function(error, data){});`
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## Data binding
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- make a "ghost call" to all circles, even if there are none already
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- `d3.selectAll('circle').data(dataArray).enter().append('circle');`
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- `.data(dataArray)` joins each element in dataArray to an element in the selection
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- `.enter()` returns the sub section of dataArray that has not been matched with DOM elements
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- `.append()` - creates a DOM element for each of the remaining dataArray elements
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- once data has been bound to elements, you can call something like `selection.attr('r', function(d,i){ })` or `selection.style('fill', function(d,i){ })`
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- callback will be executed for each DOM element
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- `d` is data for the current element
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- `i` is the index of that element in the array
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## Linear Scale
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A scale will map a data value to a visual value.
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1. Create a scale. There are many types. Here we'll use a linear scale
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```javascript
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var yScale = d3.scale.linear();
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```
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1. Set up a visual range
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```javascript
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yScale.range([height,0]);
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```
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1. Find maximum and minimum of the data set (called the "domain" of the data set)
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```javascript
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var yMax = d3.max(data, function(element){
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return parseInt(element.TMAX);
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})
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var yMin = d3.min(data, function(element){
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return parseInt(element.TMAX);
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})
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var yDomain = [yMin, yMax];
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```
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- Can combine this into one call if max/min come from same element:
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```javascript
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var yDomain = d3.extent(data, function(element){
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return parseInt(element.TMAX);
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});
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```
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1. Add the domain
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```javascript
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yScale.domain(yDomain);
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```
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1. Can check range and domain after initialization
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```javascript
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yScale.range();
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yScale.domain();
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```
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1. Can now pass a data value into the scale to get a visual value
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```javascript
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yScale(361); //returns the visual value that maps to this data value
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```
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1. Can go the opposite way
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```javascript
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yScale.invert(800); //returns the data value that maps to this visual value
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```
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## Time Scale
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1. Create the scale
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```javascript
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var xScale = d3.time.scale();
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```
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1. Set up the visual range
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```javascript
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xScale.range([0, width]);
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```
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1. Set up the date format
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```javascript
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var dateParser = d3.time.format("%Y%m%d");
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```
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- you can now parse strings of this format into dates
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```javascript
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dateParser.parse('20010101');//returns a date object
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```
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- can get a formatted string from a date object
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```javascript
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dateParser(new Date());
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```
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## Axes
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- Create the x axis
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```javascript
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var xAxis = d3.svg.axis();
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```
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- Associate the scale with the axis
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```javascript
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xAxis.scale(xScale);
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```
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- Set where on the graph the axis should appear
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```javascript
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xAxis.orient('bottom');
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```
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- Set the number of ticks
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```javascript
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xAxis.ticks(8);
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```
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- Append a group containing the axis after data has populated the scale
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```javascript
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viz.append('g').call(yAxis);
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```
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## Events
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```javascript
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select.on('mouseenter', function(data, index){
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d3.select(this); //select just element that was hovered
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console.log(d3.event); //the event object
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})
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```
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click, mouseenter and mouseleave are common
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use `d3.event.sourceEvent.stopPropagation();` when events conflict
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## Behaviors
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### Zooming
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```javascript
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//generator for a behavior
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//scale from 1 - 10
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//.on function says, when there's an event of type 'zoom', call the 'zoomed' function. Could be any event
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var zoom = d3.behavior.zoom().scaleExtent([1,10]).on('zoom', zoomed);
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var svg = d3.select('#viz-wrapper').append('svg').call(zoom);
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function zoomed(){
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console.log(d3.event.translate);//get mouse position
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console.log(d3.event.scale);//bounded by 1,10 as set up above
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viz.attr('transform', 'translate(' + d3.event.translate + ')' + 'scale(' + d3.event.scale + ')');
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}
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```
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### Dragging
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```javascript
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var drag = d3.behavior.drag()
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.on('dragstart', dragStart)
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.on('drag', drag)
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.on('dragend', dragEnd);
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//....
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dotsGroup.call(drag);
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//....
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function dragStart(d){ //d is the data for the dragged object
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d3.select(this); //the visual object
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d3.event.x; //x position of cursor
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d3.event.y; //y position of cursor
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}
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```
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You can use the xScale.invert and yScale.invert to get data from d3.event.x and d3.event.y
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