tyrell_c - 8 months ago 18

Javascript Question

I'm trying to use mapreduce to calculate monthly sales and graph with chart.js later.

Suppose I have a JSON response with fields, amount and date.

For my map function, I took out the month:

`month = _.map([items[i].transactionDate], function(date) {`

return {

lables: items[i].transactionDate.slice(5,7)

};

});

and for my reduce function ... well I didn't know what to do here.

`sum = _.reduce([items[i].amt], function(memo, num) {`

return memo + items[i].amt

});

I realized that this will eventually calculate total sum not per month. Problem is that I don't know how to relate the two functions properly.

Edit: Per request, my JSON :

`"items": [`

{

"_id": "56d1cf3704aee3c68d89cc09",

"amt": 5,

"transactionDate": "2016-02-27T16:30:47.561Z",

}

]

and what I'm trying to get out of this is sales per month on a graph. so far I've been able to project months and total sale but not sales per a specific month.

Answer

I think, simply make one loop with adding new variable

```
let result= {};
_.forEach(items, (item) => {
// get month
let month = item.transactionDate.slice(5,7);
// get amount
let amount = item.amt;
// check if we have this month in finaly object
if(month in finaly) {
// added amount
result[month] += amount;
} else {
// if this month doesn't exist added with inital value
result[month ] = amount;
}
});
```

When you can get all amount of certain month or get sum of all months

```
let allSum = _.reduce(result, (sum, amount) => sum += amount);
let amountInCertainMonth = result["01"];
```