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oshkosh
oshkosh

Reputation: 551

Lodash fp (functional programming) reduce not working how I expect it to work

Using normal lodash without fp, you'd do something like 

chain(array).map(..).reduce(...).value()

With fp, you'd do 

compose(reduce(...), map(...))(array)

I can make it work for many methods (flatten, sort, map), except reduce.

You'd expect it (lodash/fp/reduce) to work like

reduce((a,b)=>a+b, 0)([1,2,3])

But the fp version still requires 3 arguments, which doesn't make sense to me. All the other functions work like this for me, except reduce

func(...)(array)

How can I make fpreduce work like other fp functions in this manner:

compose(reduce(...), map(...), flatten(...))(array)

Upvotes: 3

Views: 4174

Answers (1)

Mulan
Mulan

Reputation: 135217

reduce takes 3 total arguments regardless of whether a functional interface is used. lodash/fp just changes parameter order and allows you to partially functions

const fp = require ('lodash/fp')

const sum = fp.reduce (fp.add, 0)

const sq = x => x * x

const main = fp.compose (sum, fp.map (sq))

console.log (main ([1,2,3,4]))
// => 30
// [1,2,3,4] => [1,4,9,16] => 0 + 1 + 4 + 9 + 16 => 30

Or as an inline composition

fp.compose (fp.reduce (fp.add, 0), fp.map (x => x * x)) ([1,2,3,4])
// => 30

Upvotes: 5

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