reduce-plus

this package provides a few extra reduce functionalitis

• reduceChunk picks N items from an array and run reduce on items, then skip one item, pick N items and reduce again until it reaches the last item.
• reduceSplit splits an array into groups with N items and run reduce on each groups. It drops last items fewer than N.
• reduceAsync runs async functions as reduce functions.
• sleep a utility function, handy to be used with reduceAsync.
• reduceObject iterates over objects' key-value pairs. It's shallow.

All functions are curried.

Install

npm install --save reduce-plus

Usage

reduceChunk

This function picks items from an array and slide one by one. It's useful for calculating moving average or min/max in a certain period.

const result = reduceChunk(fn, init, 2, [1, 2, 3, 4, 5]);

runs like this:

[1, 2, 3, 4, 5]
[1, 2]            fn(init, [1, 2])
   [2, 3]         fn(accum, [2, 3])
     [3, 4]       fn(accum, [3, 4])
        [4, 5]    fn(accum, [4, 5])

Or you can predefine the above function like so:

const reducePair = reduceChunk(fn, [], 2);
const result = reducePair([1, 2, 3, 4, 5]);

reduceSplit

This function splits an array into groups, then reduce each group.

const result = reduceSplit(fn, init, 2, [1, 2, 3, 4, 5]);

runs like this:

[1, 2, 3, 4, 5]
[1, 2]          fn(init, [1, 2])
      [3, 4]    fn(accum, [3, 4])

In this case, the last item 5 is not processed as its length fewer than 2.

This function is also curried.

reduceAsync

This function takes async functions as reducers.

const result = await reduceAsync(
                 async(accum, current) => {
                   await sleep(500);
                   return accum + current;
                 },
                 0,
                 [1, 2, 3, 4, 5]
               );

It's useful to run async functions like http requests/file operations etc. sleep function can be used with this to make it wait for some time after each iteration.

This function is also curried.

sleep

This function takes milli seconds as an argument and returns a Promise. It's handy when combining with reduceAsync.

reduceObject

This function iterates over objects' key-value pairs and pass them as a current value in each iteration. Each key-value pair takes a form [key, value] array.

const result = reduceObject(
                 (accum, [key, value]) => [...accum, `${key} is ${value}`],
                 [],
                 {foo: 'bar', bar: 'baz'}
               );

This function is also curried.

License

MIT