The functional way of creating an array from properties on an array of objects?

Question

So basically here is what I have, which works as intended -

        let newList: any[] = [];

        for (let stuff of this.Stuff) {
            newList = newList.concat(stuff.food);
        }

So basically Stuff is an array of objects where each object has a property that is another object called food. I want to go through this array of Stuff and create a new array with each instance of food within it.

I don't think the way I have done it is bad, I'm just wondering for my own curiosity how someone would have done this without the for loop.

Cheers.

Answer 1

You're looking for the map method :

const newList = this.Stuff.map(stuff => stuff.food);

You shouldn't need to use continuous reassignment to a variable, and it's certainly not functional :-) Also, using concat repeatedly is pretty inefficient, you'd better have used push within the for…of loop. But map is still simpler and better.

Answer 2

Try this approach as well using reduce method

 var arr = [[1,2,3],[4,5,6],[7,8,9]]; var output = arr.reduce( function ( prev, curr ){ return prev.concat( curr ) } ); console.log(output); 

Answer 3

You can express this nicely with an added functional primitive

const prop = x => y => y[x];

const newList = this.Stuff.map(prop('food'));