Using filter and reduce JS

Question

I am trying to use filter and reduce to get the total price of Bob's purchases for a little practice on higher order functions I'm doing. I'm given

const purchases = [{"owner":"Barry","price":103},{"owner":"Bob","price":75},
{"owner":"Bob","price":73},{"owner":"Barry","price":57},{"owner":"Barry","price":128},
{"owner":"Bob","price":119},{"owner":"Barry","price":133},{"owner":"Barry","price":27},
{"owner":"Barry","price":138},{"owner":"Bob","price":68},{"owner":"Bob","price":50},
{"owner":"Barry","price":9},{"owner":"Bob","price":123},{"owner":"Bob","price":135},
{"owner":"Barry","price":30},{"owner":"Barry","price":129},{"owner":"Barry","price":38},
{"owner":"Bob","price":133},{"owner":"Barry","price":109},{"owner":"Bob","price":115}]

Use a high order method to create to get the sum of bobsTotal.

This is what I am thinking. I am able to filter bob's purchases into an array, but I am having trouble getting the total price now. I have my reduce section commented out for now for log purposes.

let bobsTotal = purchases.filter(total=>total=purchases.owner="Bob")//.reduce((total, price) => total + price)
console.log(bobsTotal)

Any advice would be great or any other ways to do this would be great.

should be purchases.filter(purchase => purchase.owner === "Bob") — georg
– georg, Commented Apr 9, 2021 at 14:18
and for the reduce part pay attention to the second arg - it's an object, not a number — georg
– georg, Commented Apr 9, 2021 at 14:19
You are on the right track. Your callback functions for filter and reduce are incorrect. Take a look at the examples in the documentation here: filter and reduce — Will
– Will, Commented Apr 9, 2021 at 14:20
A common mistake would be .reduce((total, price) => total.price + price.price). But why do you think that the price property gets somehow automatically accessed in .reduce((total, price) => total + price)? .reduce((total, {price}) => total + price, 0) would work. — Sebastian Simon
– Sebastian Simon, Commented Apr 9, 2021 at 14:41
Thanks for the advice! It was very helpful to see the small mistakes I was making. — Justin Valdez
– Justin Valdez, Commented Apr 9, 2021 at 14:51

Matt Ellen · Accepted Answer · 2021-04-09 14:46:35Z

1

You're very close.

filter's callback needs to be a function that returns true or false.

reduce's callback's arguments are aggregate (because you are aggregating a list into one thing) and current value, and you'll want to set a default value of 0, to have something to sum from.

const purchases = [{"owner":"Barry","price":103},{"owner":"Bob","price":75},
{"owner":"Bob","price":73},{"owner":"Barry","price":57},{"owner":"Barry","price":128},
{"owner":"Bob","price":119},{"owner":"Barry","price":133},{"owner":"Barry","price":27},
{"owner":"Barry","price":138},{"owner":"Bob","price":68},{"owner":"Bob","price":50},
{"owner":"Barry","price":9},{"owner":"Bob","price":123},{"owner":"Bob","price":135},
{"owner":"Barry","price":30},{"owner":"Barry","price":129},{"owner":"Barry","price":38},
{"owner":"Bob","price":133},{"owner":"Barry","price":109},{"owner":"Bob","price":115}]

let bobtot = purchases.filter(p => p.owner === 'Bob').reduce((sum, p) => sum+p.price, 0);

console.log('bob\'s total:', bobtot);

answered Apr 9, 2021 at 14:46

Matt Ellen

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1 Comment

Justin Valdez Over a year ago

Thanks Matt. This worked great and makes sense. I'm glad I was at least on the right track, just needed a little nudge from all you great overflowers!

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