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  • License MIT

reduce objects deeply, call reducer for every nested node in object tree

Package Exports

  • deep-reduce

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (deep-reduce) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

Build Status npm version

deep-reduce

Reduce objects deeply, call reducer for every nested node in object tree. Use deepReduce for transforming/getting values from awfully nested objects. deepReduce also traverse arrays.

Install

npm i deep-reduce

Usage

Try example in browser.

const deepReduce = require('deep-reduce')
const deepEqual = require('assert').deepEqual

// let nested leaf values be equal to their path, for demonstration purpose
let deepNestedObject = {
  a: 'a',
  b: { c: 'b.c' },
  c: [
    'c.0',
    {
      d: 'c.1.d',
      e: [
        'c.1.e.0'
      ]
    }
  ]
}

// store all values which are strings to reduced[path].
let flattenStrings = (reduced, value, path) => {
  if (typeof value === 'string') {
    reduced[path] = value
  }
  return reduced
}

// the reduced value is returned
let reduced = deepReduce(deepNestedObject, flattenStrings)

// we should now have this object
deepEqual(reduced, {
  'a': 'a',
  'b.c': 'b.c',
  'c.0': 'c.0',
  'c.1.d': 'c.1.d',
  'c.1.e.0': 'c.1.e.0'
})

Root object may be an array also:

deepReduce([{a: 1},{b: 2},{a: 3}], (r,v) => typeof v === 'number' ? r + v : r, 0)
// 6

Here is how you would collect all items of nested arrays at some specific path:

// we want to get contents from all packets
let transport = {
  id: 'A8811',
  packages: [
    {
      id: 'P100',
      contents: [
        {
          id: 'R88',
          name: 'resistor'
        },
        {
          id: 'C99',
          name: 'capacitor'
        }
      ]
    }, {
      id: 'P101',
      contents: [
        {
          id: 'C96',
          name: 'coil'
        }
      ]
    }
  ]
}

let contents = deepReduce(transport, (reduced, value, path) => {
  if (path.match(/packages\.\d+\.contents\.\d+$/)) {
    // path is packages.n.contents.m
    // item n in packages array
    // item m in contents array
    reduced.push(value)
  }
  return reduced
}, [])  // start with an empty array

// [ { id: 'R88', name: 'resistor' },
//   { id: 'C99', name: 'capacitor' },
//   { id: 'C96', name: 'coil' } ]

API

deepReduce takes 5 arguments. 2 mandatory and 3 optional:

deepReduce (
  obj: object,
  reducer: (reduced: any, value: any, path: string, root: object) => any,
  reduced = {},
  path = '',
  thisArg = {}): any

Arguments

  • obj Object to traverse.

  • reducer Function to call with every value in obj-tree. See section below for reducer function signature.

  • reduced Initial value of reduced passed to reducer. Defaults to empty object {}.

  • path Path to root, start traversing here. Nice to omit looping through parts of obj.

    Example:

    deepReduce({ a: [1,2,3], b: { c: [3, 3] } }, (reduced, val) => reduced + val, 1, 'b.c')
// only traverses b.c, returns 1 + 3 + 3 = 7

  • thisArg Bound to reducer as this.

Arguments for reducer function

The reducer function is called with these arguments:

(reduced: any, value: any, path: string, root: object) => any
  • reduced Initial or current reduced value.
  • value Value of current node.
  • path Path to current value.
  • root Root object passed to deepReduce as obj.

The reducer should return the reduced value.

Performance

deep-reduce traverses every node of a 149 kb JSON in 10 milliseconds on a macbook air 2013 i5 1.3GHz, see test.js.

You can omit traversal of parts of the object tree with defining a start path:

deepReduce(object, reducer, initialValue, 'start.at.this.path')

...which may give some performance gains.

Development

git clone https://github.com/arve0/deep-reduce
cd deep-reduce
npm start  # watches index.ts and builds on any change
npm test  # runs node test.js

License

MIT © 2017 Arve Seljebu