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# MapStream
Refactored out of [event-stream](https://github.com/dominictarr/event-stream)
##map (asyncFunction[, options])
Create a through stream from an asyncronous function.
``` js
var map = require('map-stream')
map(function (data, callback) {
//transform data
// ...
callback(null, data)
})
```
Each map MUST call the callback. It may callback with data, with an error or with no arguments,
* `callback()` drop this data.
this makes the map work like `filter`,
note:`callback(null,null)` is not the same, and will emit `null`
* `callback(null, newData)` turn data into newData
* `callback(error)` emit an error for this item.
>Note: if a callback is not called, `map` will think that it is still being processed,
>every call must be answered or the stream will not know when to end.
>
>Also, if the callback is called more than once, every call but the first will be ignored.
##Options
* `failures` - `boolean` continue mapping even if error occured. On error `map-stream` will emit `failure` event. (default: `false`)
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