Understand why Transducers can Improve Performance

Write Reducers for Different Data Types


Understand Transformer Functions

Rewrite Map and Filter as Reducers

Create Map and Filter Transducers

Improve Composition with the Compose Combinator

Transduce over any Iteratable Collection

Make an Into Helper to Remove Boilerplate and Simplify our Transduce API

Transduce When the Collection Type is an Object

Create a Sequence Helper to Transduce Without Changing Collection Types

Add the Transducer Protocol to Support Arbitrary Data Types as our Target Collections

Measure the Performance of our Transducers

Use Transducers in Production

Quickly Transform Data with Transducers

We've seen how we can `transduce` from arrays or other iterables, but plain objects aren't iterable in Javascript.
In this lesson we'll modify our `transduce()` function so that it supports iterating from plain objects as well, treating each key value pair as an entry in the collection.

To do this we'll be using a **lodash** function called [entries](https://lodash.com/docs/4.17.4#toPairs). 

https://app.egghead.io/api/v1/lessons/egghead-transduce-when-the-collection-type-is-an-object/subtitles

[00:00] If the collection we're transducing over is an object, our transduce function isn't going to work. The reason for this is object aren't iterables, so this for-of loop is just going to throw an error. To add support for plain object iteration, let's convert our objects to array pairs.

[00:17] Let's rename this collection argument, and then, before our loop, we'll create a variable called Collection. Here we want to check if our collection is a plain object. I'll call isPlainObject, which will take our collection and, if that's true, will call the Lodash helper entries with our collection, but otherwise will just return the collection.

[00:41] Entries is the same as the newer object.entries, but I'm running a version of Babel where that's not supported. That's why I'm using entries from Lodash. What it does is, let's say you have an object with keys and values, then after you call entries, what you're going to get back instead is an array where each element is another array, where the first element is the key and the other one is the value. That's why, after calling entries here, we'll still be able to iterate through our collection.

[01:14] To test this out, let's create our own version of object.values. We'll call this object Values. The point of this function is to take a source object and pour all of the values into an array. We'll use our Into helper. Our target will be an array. Our transformer should just pull out the values from the object. We'll call map. Here we'll get an array with a key and the value, and we just want to return the value, which is that index one. Our source will be the object.

[01:45] Let's try this out. If we call object Values with an object, we should get an array back with just our numbers. We got undefined as our result, so we've missed something. Since we're using brackets in our object values function, we haven't got an implicit return, so let's add that in. Now we get our array with our elements one and two.

Transduce When the Collection Type is an Object

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Quickly Transform Data with Transducers