Grouping and summing array objects

I’m having a data sample like this this.userData = [ {id:1, category: ‘Food’, amount: 30, pDate: ‘2021-01-13’, description: ‘test desc’}, {id:2, category: ‘Fuel’, amount: 10, pDate: ‘…

Why NaN’s reduce return?

I commented out the return sum, on purpose, because it does not work as expected. If I remove return sum, it returns the right average. But this is what I don’t understand: when it enters the if in …

Testing whether you reach an array’s last item when using reduce() in Javascript

I am trying to implement the equivalent of .join() using .reduce() to answer a quiz on executeprogram.com. My code passes the tests, but it seems ugly. The specific issue that I have solved in an ugly …

What is the flow of execution with this compose function passed into Javascripts reduce?

I just want to know how reduce works in the case of code below(which was provided by a stackoverflow user in my previous question, i’m asking this question as his code snippet led to me having more …

JS reduce: object accumulator titles

I am experimenting with the reduce function at the moment and wondering if I can tailor the accumulator’s keys’ name to be a specific value? For example, the below code returns {16 years of experience:…

Javascript: Using reduce() to find min and max values?

I have this code for a class where I’m supposed to use the reduce() method to find the min and max values in an array. However, we are required to use only a single call to reduce. The return array …

reduce function composed of map function in JavaScript

Say we have and want to reduce() it like Now, I want to compose reduce() function itself from map() function. How would you do that? What is the smartest way? Edit: In the comments and answers, many have claimed fold/reduce can compose map, in shallow level, that can be true, however, in category theory, fundamentally reduce/fold is generalized to Catamorphism and it’s all about functors (map), and it’s called F-algebra. https://en.wikipedia.org/wiki/Catamorphism https://en.wikipedia.org/wiki/F-algebra Answer If you’re trying to build the map function using reduce, you could do the following (The example I’m providing will use built-in functions and work for arrays