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https://github.com/francisrstokes/simple-transduce
A really simple transducer module to easily convert map-filter-reduce chains to single pass transducers.
https://github.com/francisrstokes/simple-transduce
functional javascript library transducer
Last synced: about 1 month ago
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A really simple transducer module to easily convert map-filter-reduce chains to single pass transducers.
- Host: GitHub
- URL: https://github.com/francisrstokes/simple-transduce
- Owner: francisrstokes
- Created: 2017-11-29T14:52:02.000Z (about 7 years ago)
- Default Branch: master
- Last Pushed: 2017-11-30T12:41:34.000Z (about 7 years ago)
- Last Synced: 2024-10-29T18:12:54.546Z (3 months ago)
- Topics: functional, javascript, library, transducer
- Language: JavaScript
- Homepage:
- Size: 4.88 KB
- Stars: 3
- Watchers: 2
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# simple-transduce
A really simple transducer module to easily convert map-filter-reduce chains to single pass transducers.
## Install
```bash
npm install simple-transduce
```
## Concept
Take some existing code like this:
```javascript
const collection = [1,2,3,4,5,6,7,8,9,10];
const multiplyBy5 = (value) => value + 5;
const notMultipleOf3 = (value) => value % 3 !== 0;
const square = (value) => value * value;
const notMultipleOf4 = (value) => value % 4 !== 0;
const newCollection = collection
.map(multiplyBy5)
.filter(notMultipleOf3)
.map(square)
.filter(notMultipleOf4);
// Result = [ 49, 121, 169 ]
// Total elements of all intermediate collections, including original: 34
```
This works fine, and the original list is transformed from 10 members to just 3 in the end, as expected.
However this transformation happens over multiple intermediate collections, meaning while the original array has 10 elements,
you actually iterate over 4 collections of 10, and thus (potentially) 40 elements. A transducer allows for a generic method that
lets you do just a single pass of the 10 elements without sacrificing the clarity of having those 4 distinct transformation functions.
### Converting map-filter to transduce
```javascript
const st = require('simple-transduce');
const collection = [1,2,3,4,5,6,7,8,9,10];
const multiplyBy5 = st.mapTransducer((value) => value + 5);
const notMultipleOf3 = st.filterTransducer((value) => value % 3 !== 0);
const square = st.mapTransducer((value) => value * value);
const notMultipleOf4 = st.filterTransducer((value) => value % 4 !== 0);
const transducer = st.compose(multiplyBy5, notMultipleOf3, square, notMultipleOf4);
const newCollection = st.reduce(transducer(st.concat), [], collection);
// Result = [ 49, 121, 169 ]
// Total elements of all intermediate collections, including original: 10
```
Note that `compose`, `reduce` and `concat` are not special functions - they are found in many common functional libraries (and lodash)
and are thus interchangable with those.
## Functions
- `mapTransducer(mapFunction)` -> creates a composable transducer from the map function
- `filterTransducer(filter)` -> creates a composable transducer from the filter function
- `reduce(reducerFunction, start, collection)` -> generic reduce
- `compose(...fns)` -> generic compose. Example: `compose(f, g) = (x) => f(g(x))`
- `pipe(...fns)` -> generic pipe (compose inverse). Example: `pipe(f, g) = (x) => g(f(x))`
- `concat(acc, item)` -> generic concat reducer
- `sum(acc, item` -> generic sum reducer