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benwells/reduce-example.js

Created May 12, 2016 13:40
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Using Array.reduce to sum a property in an array of objects
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reduce-example.js
var accounts = [
{ name: 'James Brown', msgCount: 123 },
{ name: 'Stevie Wonder', msgCount: 22 },
{ name: 'Sly Stone', msgCount: 16 },
{ name: 'Otis Redding', msgCount: 300 } // Otis has the most messages
];
// get sum of msgCount prop across all objects in array
var msgTotal = accounts.reduce(function(prev, cur) {
return prev + cur.msgCount;
}, 0);
console.log('Total Messages:', msgTotal); // Total Messages: 461
@RihabBerry
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this is the genius solution!

@leonelmatsinhe
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In ES6: const msgTotal = accounts.reduce((prev, cur) => prev + cur.msgCount, 0);

Thanks dude!

@stoicalpirate
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Thanks - super useful!

@saurav2811
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Is it possible to use reduce if I have a calculation trough-out multiple properties like this:

var items = [
  { name: 'Item 1', amount: 123, discount: 0.1 },
  { name: 'Item 2', amount: 22, discount: 0.1 },
  { name: 'Item 3', amount: 16, discount: 0.2 },
  { name: 'Item 4', amount: 300, discount: 0 }
];

So I have to do something like this:

total = sum_all_items(amount - (amount * discount))

simplify it as total = sum_all_items(amount * (1 - discount))
OR
first, just make, discount = 1 - discount, and then, sum(amount * discount)

@Bizzle-Dapp
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Banging. Nice one, mate.

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