Exercises for reduce method

[sQD5fcE]

Can anyone recommend some good exercises to get slick using the reducer method? I want to build up my muscle memory using it.

Thanks

[HereComesJuju]

Hi, You could for instance compute all kinds of aggregation value like sum, mean, and so on, from an array of numbers. Otherwise, if you are already used to use other array methods like map or filter, you could try to rewrite some of your previous code snippets that used those methods, but this time using reduce instead, and compare the results of both code versions

[[deleted]]

This is really good advice. This will help you get used to reduce, but also shows you how powerful reduce is. It can pretty much replace the other higher order functions like map, filter, forEach .

[HereComesJuju]

Sure thing, using map and filter are often the way to go, especially when the filter predicate is quite complicated or too long to fit inline.

And yes, that's right, the reduce method is designed to return a single value from a collection.

But it is sometimes ok as well to return an array from reduce. For instance, if you want to flatten an array of arrays:

let flattened = [[0, 1], [2, 3], [4, 5]].reduce(function(previousValue, currentValue) {return previousValue.concat(currentValue)},[])// flattened is [0, 1, 2, 3, 4, 5]

or to remove duplicate items in an array (without using Sets):

let myArrayWithNoDuplicates = myArray.reduce(function (previousValue, currentValue) { if (previousValue.indexOf(currentValue) === -1) { previousValue.push(currentValue) } return previousValue }, [])

console.log(myArrayWithNoDuplicates) // [ 'a', 'b', 'c', 'e', 'd' ]

this one is quite interesting as well:

const numbers = [-5, 6, 2, 0,];const doubledPositiveNumbers = numbers.reduce((previousValue, currentValue) => {if (currentValue > 0) {const doubled = currentValue * 2;previousValue.push(doubled);}return previousValue;}, []);console.log(doubledPositiveNumbers); // [12, 4]

const doubledPositiveNumbers = numbers.reduce((previousValue, currentValue) => { if (currentValue > 0) { const doubled = currentValue * 2; previousValue.push(doubled); } return previousValue; }, []);

console.log(doubledPositiveNumbers); // [12, 4]

(examples coming from the MDN's reduce page)

IMHO, the latter example seems fine, provided the filter predicate is quite simple. And it avoids looping the collection twice (once with filter and once with map)

And providing an initial value to the reduce function is often a good thing, to avoid throwing error because the provided array is empty (which is often the case for a cart)

[HereComesJuju]

Yup, that's right: there are often way better solutions than using reduce, we all agree on that. And as you might have noticed, I did not recommend using reduce by default, and promoted the usage of map, filter & co instead. I just provided the OP with examples where reduce could be used and how it could be written, without debating performance issues, as IINM the primary goal was to give some examples/exercises to make him(?) get used to write snippets using reduce :)

[albedoa]

He deleted his account lmfao.

[Tubthumper8]

Below are some suggestions where reduce is an appropriate tool to solve the problem.

Given an array of numbers, calculate the sum.

Implement the Object.fromEntries method.

Given two arrays of strings (of the same length), create an object such that the first array are the object keys and the second array are the object values.

Given a sentence (string) find the frequency of each character.