I am trying to read a csv file with d3 in a node-environment. I am kind of confused what the "best-practice"-way therefore is and why I keep on getting a TypeError.
I know that for some module of d3a environment that supports fetch must be present. Therefore my code at the moment looks like this:
import * as d3 from "d3";
import fetch from "node-fetch";
global.fetch = fetch;
let data_path = "flightCodes.csv";
// would a d3.csvParse(fs.readFileSync(data_path)) be better?
let data = await d3.csv(data_path, function (err, dat) {
if (err) {
console.log(err);
} else {
console.log(dat);
}
});
console.log(data);
The csv file lives in the same folder and looks like this:
orig,dest,orig_codes,dest_codes
Paris,Lyon,"BVA, ORY, CDG",LYS
Paris,Bordeaux,"BVA, ORY, CDG",BOD
Paris,Nantes,"BVA, ORY, CDG",NTE
Madrid,Barcelona,MAD,BCN
Lisboa,Porto,LIS,OPO
My package.json looks like this:
{
"name": "name",
"version": "1.0.0",
"description": "",
"type": "module",
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1"
},
"keywords": [],
"author": "",
"license": "ISC",
"dependencies": {
"d3": "^7.2.0",
"d3-fetch": "^3.0.1",
"node-fetch": "^3.1.0"
}
}
When I do a node script.js, I get the following and I do not completely understand why. Anybody might have an idea?
node:internal/errors:464
ErrorCaptureStackTrace(err);
^
TypeError [ERR_INVALID_URL]: Invalid URL
at new NodeError (node:internal/errors:371:5)
at onParseError (node:internal/url:552:9)
at parse (<anonymous>)
at new URL (node:internal/url:632:5)
If the file you're referencing is not available through a URL, then d3.csv (which uses fetch) cannot find it. Internally, d3.csv fetches the data and then calls d3.csvParse to parse it, so you can do the same!
let data = d3.csvParse(fs.readFileSync(data_path));
In addition, there was another problem with your code. The signature d3.csv(path, callback) is deprecated. Instead, it will execute the second argument on every row as a parse function. The correct way to call it would be d3.csv(path).then(callback) or
const data = await d3.csv(path);
callback(data);