在 ramda 中组合函数

Question

I have a function which takes two arguments, I want to curry it because it used more that one time in code. here is the function :

const discount = R.sum(R.map(R.propOr('0', 'discount'), invoiceArr));

now I want to give argument's (' discount ' & invoiceArr ) and return the value. I have try another way which like below:

const sumByPropName = R.curryN(2, R.compose(R.sum, R.pluck));

but this way has not propOr method.

Answer 1

There's a number of ways you can go about this. Assuming you still want the function curried, the easiest way is to just make add the arguments

const sumByPropName = R.curry((prop, items) => R.compose(R.sum, R.map(R.propOr(0, prop)))(items))

An alternative is to use R.defaultTo to map over the undefined values and set them all to 0 , before passing to sum

const sumByPropName = R.curryN(2, R.compose(R.sum, R.map(R.defaultTo(0)), R.pluck))

Lastly, you could create a pluckOr function yourself, keeping sumByPropName a bit cleaner (although there's surely a nicer way to write pluckOr )

const pluckOr = R.curry((defaultVal, propName, items) => R.map(R.propOr(defaultVal, propName), items))
const sumByPropName = R.curryN(2, R.compose(R.sum, pluckOr(0)))