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calculate mean standard deviation in one pass


a reduce function that calculates mean and standard deviation in one pass

I first wrote this module a long long time ago, and i used an object oriented api. Today I needed to serialize a stats output to JSON, and then later parse it, and keep using it. Continuing to use an OO api would mean a bunch of glue code, so I rewrote it as a reduce function.

var stats = require('statistics')
=> {
  mean: 2,
  stdev: 0.8164965809277263,
  count: 3,
  sum: 6,
  sqsum: 14

you probably only want to have the mean and stdev, the other fields are necessary for the reduce function however.

sometimes, a mutating reduce is prefured. this eases garbage collection, and allows you to maintain a reference to an updating value.

otherwise the api is the same.

statistics@2 and earlier used an object oriented api, but then I needed to serialize and parse a stats object and keep using it. That was incredibly easy with a reduce function, but would have meant a bunch of ugly glue code with OO.