Map Reduce for nodejs

use nosql style map reduce functions to iterate over data in node.

1 function:

var mapR = require('map-reduce')

mapR({
  on: collection to iterate over (can be an object or an Array)
  map: iteration function (optional, defaults to mapR.identity
  reduce: reduction function (optional, defaults to mapR.collect)
  init: initial value for collection arg in reduce step, default to undefined
  done: callback function
})

##map (emit, value, key) ##

calling emit(value[,key,etc...]) will send args to the reduce function.

map-reduce is async, call emit.next() to go to the next item. or, emit.done() to stop processing more items.

if the values to be emitted are passed into emit.next or emit.done that is like calling emit(args); emit.next(), or emit(args); emit.done()

##reduce (collection, value[, key,etc...]) ##

reduce will be called with a collection which is either,

1. the return value of the previous reduce call
2. the .init value you supplied to mapR
3. undefined

the other arguments are the values you called emit with.