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-reduceUsage
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)
// 6Here 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 = {}): anyArguments
-
objObject to traverse. -
reducerFunction to call with every value inobj-tree. See section below forreducerfunction signature. -
reducedInitial value ofreducedpassed toreducer. Defaults to empty object{}. -
pathPath to root, start traversing here. Nice to omit looping through parts ofobj.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
-
thisArgBound to reducer asthis.
Arguments for reducer function
The reducer function is called with these arguments:
(reduced: any, value: any, path: string, root: object) => any-
reducedInitial or current reduced value. -
valueValue of current node. -
pathPath to current value. -
rootRoot object passed todeepReduceasobj.
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.jsLicense
MIT © 2017 Arve Seljebu
