Add async.transform

[megawac]

Similar concept to https://lodash.com/docs#transform this is a function with several fundamental differences to async.reduce:

• parallel
• dynamically interprets memo (signature arr|obj, arr|obj, fn, fn -> arr|obj) which can be useful for recursive cases
• provides key to iterator function

[qsona]

Hi, I use lodash.transform very often and think it is also useful on async. neo-async already has the same method, but, a worring factor is that the order of the arguments is not same as that, which places the memo arg at the last. lodash.transform also places it at last so I think it should maintain same order as lodash.transform. How do you think of it?

[megawac]

I'm not sure, I was attempting to be consistent with the reduce argument
order

On Mon, Aug 24, 2015 at 10:00 PM, qsona [email protected] wrote:

Hi, I use lodash.transform very often and think it is also useful on async.
neo-async already has the same method, but, a worring factor is that the
order of the arguments is not same as that, which places the memo arg at
the last. lodash.transform also places it at last so I think it should
maintain same order as lodash.transform. How do you think of it?

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#892 (comment).

[qsona]

I see. I didn't know that the arguments order of async.reduce is different from that of Array.prototype.reduce.

[aearly]

👍 once we figure out what the arg order should be. Also seems related to #873

[megawac]

yeah, both array and object maps can be implemented very easily through
transform

On Mon, Aug 24, 2015 at 11:32 PM, Alexander Early [email protected]
wrote:

[image: 👍] once we figure out what the arg order should be. Also seems
related to #873 #873

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#892 (comment).

[megawac]

/cc @suguru03

I think consistency with reduce argument orders is important but I can be swayed on this note

[qsona]

First of all, I totally agree that the arguments order of async.transform should be same as that of async.reduce.

Next, I think that the arguments order of reduce might be not proper. As that of Array.prototype.reduce is iterator, initialValue, async should follow the JavaScript API rules, so collection, iterator, initialValue, callback is the best order, isn't it?

This order is different from neo-async#transform too.
And of course, the major version up is required if we want to change async.reduce API. If it is not possible, I think it should follow the current order of async.reduce.

[suguru03]

Almost all functions of lodash take optional arguments after required arguments, so I have developed neo-async.transform which take an accumulator of optional argument to last.
Because initial value of async.reduce is optional, I want to place accumulator as the last and think that collection, iterator, callback, [accumulator] order is desirable.
Even if they takes anyway, I'm going to fix to take same argument order with your choice.

[aearly]

I'd prefer to have it async.reduce(arr, iterator, [accumulator,] callback). Following the node convention of having the callback as the last arg is more important that having optional args last. We can define async.transform with that signature, and then perhaps change async.reduce in a major release?

[qsona]

+1 😉

[megawac]

Yeah, lets get 1.4.2 shipped soon and put this in v2 with the reduce change

On Mon, Sep 28, 2015 at 8:55 PM, qsona [email protected] wrote:

+1 [image: 😉]

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#892 (comment).

[aearly]

We'll fix the arg ordering later.