Merging arrays that hold CSV data into one object array

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I've taken influence from this post to store CSV files in individual arrays, and it works. I'm looking to add about 8 more arrays that each hold the contents of a CSV file.

But how can I merge these arrays into one array of objects? Having an array of objects is critical for my subsequent application of these arrays. What I have so far is below, but I'm not sure if it is correct or not?

Any help would be appreciated.

var dataCSV;
var dataCSV2;

var collection = {dataCSV, dataCSV2};

d3.csv("data/csv1.csv", function(data) {
    data.forEach(function(d) {
        d.word = d.word;
        d.frequency = +d.frequency;
})
    dataCSV = data;
    console.log(dataCSV);
});

d3.csv("data/csv2.csv", function(data) {
    data.forEach(function(d) {
        d.word = d.word;
        d.frequency = +d.frequency;
    })
    dataCSV2 = data;
    console.log(dataCSV2);
});

function merge(data1, data2) {
    collection = {data1, data2};
    console.log(collection);
}

merge(dataCSV, dataCSV2);

Ideally, I'd like the output of collection to be: 

collection {
    dataCSV {
        word: ..., frequency: ...,
        word: ..., frequency: ...
    },
    dataCSV2 {
        word: ..., frequency: ...,
        word: ..., frequency: ...
    }
 }
d3.js csv arrays javascript
1 Answers

Instead of repeating yourself, create a single method that gets the data, formats it, and returns a promise. Then collect the results of several promises using Promise.all(). Then you can collect both arrays in an object.

Example (not tested):

const getCsv = (url) => new Promise((resolve) => {
  d3.csv(url, function(data) {
    data.forEach(function(d) { // you can use a Array.map() instead for a cleaner solution
      d.word = d.word;
      d.frequency = +d.frequency;
    })

    resolve(data);
  });
});

Promise.all([ // load both csvs, and wait for the results of both
  getCsv('data/csv1.csv'),
  getCsv('data/csv1.csv')
])
.then(([dataCSV, dataCSV]) => { 
  const collection = { dataCSV, dataCSV2 };
  console.log(collection );
});
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