JavaScript - Unable to retrieve individual elements from an array generated by parsing a CSV file

Question

JavaScript - Unable to retrieve individual elements from an array generated by parsing a CSV file

I have a csv file generated by a database that I need to convert into an array. The file is in the same folder as my script.

Here is how the csv file is formatted: (I am unable to show the original data)

https://i.sstatic.net/SgKt1.png

https://i.sstatic.net/PxiYW.png

I came across a d3 script that helps me import data from the csv file. This is what my code looks like:

var myArray= []

d3.csv("data.csv", function(data){
    myArray.push(data)
});

console.log(myArray)

Now, I can view the array in the console by using the command "myArray". It looks like this:

https://i.sstatic.net/ZA7Tw.png

https://i.sstatic.net/usHGL.png

When I inspect the array, I see multiple objects structured like this:

0: { "HeaderA": "A1", "HeaderB": "B1", "HeaderC": "C1", … }

1: { "HeaderA": "A2", "HeaderB": "B2", "HeaderC": "C2", … }

2: { "HeaderA": "A3", "HeaderB": "B3", "HeaderC": "C3", … }

and so forth...

My issues:

When I type myArray[0] in console, I see the first object but cannot access its elements (A1,B1,C1...). Why? How?
I encounter an error when trying to use myArray[0] in my code to loop through the objects: "ReferenceError: array is not defined"
I am aiming to structure the array like this...

[["HeaderA", "A1", "A2", "A3", "A4" "A5"],
 ["HeaderB", "B1", "B2", "B3", "B4" "B5"],["HeaderC", "C1", "C2", "C3", "C4" "C5"],...]

...in order to effectively work with the data. However, I am unsure how to achieve this since I cannot access individual elements?

Thank You :)

javascript arrays csv d3.js

Answer 1

Answer №1

While not the quickest or most efficient method, here is a breakdown of steps to achieve the desired format:

Create a set of unique keys to identify which keys are required.
Map the keys and extract the corresponding values from the original array.

For example, consider the following input:

var parsedArray = [
    { "HeaderA": "A1", "HeaderB": "B1", "HeaderC": "C1" },
    { "HeaderA": "A2", "HeaderB": "B2", "HeaderC": "C2" },
    { "HeaderA": "A3", "HeaderB": "B3", "HeaderC": "C3" }
];

Inspired by this example, here is the code to achieve the desired format:

const uniqueKeys = [...new Set(...parsedArray.map(i => Object.keys(i)))];

const res = uniqueKeys.map(k => {
    return [k, ...parsedArray.map(i => i[k]).filter(i => i !== null && i !== undefined)];
});
console.log(res);

Explanation:

[...new Set(...parsedArray.map(i => Object.keys(i)))];

The spread operator (...) is used to expand the values as arrays are iterable. The map function gathers all the keys from each object (HeaderA, HeaderB, HeaderC) and the new Set ensures uniqueness, resulting in an array like: ["HeaderA","HeaderB","HeaderC"].

In the second part, a new array is created for each unique key. The header is set as the first element, followed by all elements in the original array with that respective key.

A working fiddle can be found here: https://jsfiddle.net/jde37v64/1/

Additionally, if you're writing values asynchronously within a callback, ensure it is done within the function block like so:

var myArray= []

d3.csv("data.csv", function(data){
    myArray.push(data)
    console.log(myArray)
    // Write your code here, NOT OUTSIDE OF THIS FUNCTION BLOCK.
});

This is crucial as myArray is only accessible inside the callback scope.

Answer 2

While not the quickest or most efficient method, here is a breakdown of steps to achieve the desired format:

Create a set of unique keys to identify which keys are required.
Map the keys and extract the corresponding values from the original array.

For example, consider the following input:

var parsedArray = [
    { "HeaderA": "A1", "HeaderB": "B1", "HeaderC": "C1" },
    { "HeaderA": "A2", "HeaderB": "B2", "HeaderC": "C2" },
    { "HeaderA": "A3", "HeaderB": "B3", "HeaderC": "C3" }
];

Inspired by this example, here is the code to achieve the desired format:

const uniqueKeys = [...new Set(...parsedArray.map(i => Object.keys(i)))];

const res = uniqueKeys.map(k => {
    return [k, ...parsedArray.map(i => i[k]).filter(i => i !== null && i !== undefined)];
});
console.log(res);

Explanation:

[...new Set(...parsedArray.map(i => Object.keys(i)))];

The spread operator (...) is used to expand the values as arrays are iterable. The map function gathers all the keys from each object (HeaderA, HeaderB, HeaderC) and the new Set ensures uniqueness, resulting in an array like: ["HeaderA","HeaderB","HeaderC"].

In the second part, a new array is created for each unique key. The header is set as the first element, followed by all elements in the original array with that respective key.

A working fiddle can be found here: https://jsfiddle.net/jde37v64/1/

Additionally, if you're writing values asynchronously within a callback, ensure it is done within the function block like so:

var myArray= []

d3.csv("data.csv", function(data){
    myArray.push(data)
    console.log(myArray)
    // Write your code here, NOT OUTSIDE OF THIS FUNCTION BLOCK.
});

This is crucial as myArray is only accessible inside the callback scope.

JavaScript - Unable to retrieve individual elements from an array generated by parsing a CSV file

Answer №1

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