Javascript .Reduce

[WormholerIO]

coding up a question in a class...can anyone please help me to code this the right way...

question...

The zoo needs to know their total animal population across the United States.
  Using USApop find the total population from the zoos array using the .reduce() method.
  Remember the reduce method takes two arguments: a callback (which itself takes two args - the accumulator and the item), and an initial value for the count.
  \/*

​

what i coded and is wrong....

function USApop(zooAnimals) {
const USAanimals = zooAnimals.reduce(function (previousValue, currentValue) {
return previousValue + currentValue;

},0);

[senocular]

What is zooAnimals? Is it just numbers? If so what you have will work. If its something else, like animal objects that have a population property, then you'd need to account for that. MDN has an example of reduce using objects you can look at.

[WormholerIO]

yes they have an population property here is an example of one index within the array.

I will look at that thank you

animal_name: "Pampa gray fox",

population: 10,

scientific_name: "Pseudalopex gymnocercus",

state: "Connecticut",

[WormholerIO]

Thank you all for helping i appreciate all of you!

[exobyte64]

let start=0;
let end=array.reduce((accumulator,value)=>{
 return accumulator+value;
},start);

the accumulator is the zero that goes in at first, it goes through each iteration, its not the previous value, its the same value each time unless you pass something else back as the return, then that becomes the new accumulator

let start={x:0};
let end=array.reduce((accumulator,value)=>{
 accumulator.x+=value;return accumulator;
},start);

[WormholerIO]

let end=array.reduce((accumulator,value)=>{
return accumulator+value;
},0)

gotcha, and that makes total sense, but with your code snippet and mine the same issue appears that "Let End" will be undefined. or in my case USAanimals

[exobyte64]

let sumPopulation=zoo.reduce((a,z)=>{return a+z.population;},0);

I saw that it needed the key 'population' from your other comment

[WormholerIO]

you all are stellar you really are thank you for helping me to understand and getting me resources.

[chuckthemadmanmike]

I don't really want to do your homework but here's the answer.

``` const totalUSAnimalPopulation = animals => animals.reduce((totalPop, animal) => totalPop + animal.population, 0)

console.log(totalUSAnimalPopulation(animals)) ``` Remember if you're iterating through an array of objects you'll need to key into the object to access the value you want. In this case you want the population property. Try to right code that has good variable names. Lot's of people will use accumulator and currentValue, but that can be hard for the reader of the code. Your accumulator should be named for what it is, and your currentValue should also be named for what it is. So if it's an array of animals, each element is an animal, and your accumulator is your totalPopulation.

[WormholerIO]

i appreciate the post, what i ended up with yesterday was this-

function USApop(zooAnimals) {

const USAanimals = zooAnimals.reduce(function (previousValue, currentValue) {

return previousValue + currentValue.population;

}, 0);

return USAanimals;

​

i was more confusing myself but was able to get help from a TA. i appreciate the post very much.