I am trying to loop through an object that has been parsed from a CSV file of Locations, and Lat/Lng pairs. But when I loop through this object, the first loop returns my object with all the values as undefined. My code is as follows:
import React, { Component, useState, useEffect } from 'react';
import { LatLng } from 'leaflet';
import { Map, TileLayer, CircleMarker, Popup, Marker } from 'react-leaflet';
import CovidCasesClean from './CovidCasesClean.csv';
import Papa from 'papaparse';
export default function PlaceMarker() {
const latlng = [null];
const [rows, setRows] = React.useState([])
const [data, setData] = React.useState({});
React.useEffect(() => {
async function getData() {
const response = await fetch('/data/CovidCasesClean.csv')
const reader = response.body.getReader()
const result = await reader.read() // raw array
const decoder = new TextDecoder('utf-8')
const csv = decoder.decode(result.value) // the csv text
console.log(csv)
const results = Papa.parse(csv, { header: true, skipEmptyLines: true}) // object with { data, errors, meta }
console.log(results)
const rows = results.data
console.log(rows)
// array of objects
setRows(rows)
rows.map((item, i) => {
const rowObj = {item}
//console.log(rowObj)
console.log(i)
setData({
...data, key: i, ...data, location: rowObj.item.Location, ...data, latitude: parseFloat(rowObj.item.Latitude), ...data, longitude: parseFloat(rowObj.item.Longitude), ...data, cases: parseFloat(rowObj.item.TotalCases)
})
})
}
getData()
}, []) // [] means just do this once, after initial render
return (
<div>{console.log(data.key, data.location, data.latitude, data.longitude, data.cases)}</div>
)
}
When the console line: <div>{console.log(data.key, data.location, data.latitude, data.longitude, data.cases)}</div>
is ran, the first result returns:
undefined undefined undefined undefined undefined
whereas the second run through returns the correct object like so:
0 Barking and Dagenham 53.546299 -1.46786 18
This causes my creating a marker object to fail as the first object is not a latlng pair, I have been trying to create markers like so:
<Marker position={(data.longitude, data.latitude)}>
<Popup>
<span>
A pretty CSS3 popup.
<br />
Easily customizable.
</span>
</Popup>
</Marker>;
This is where the error occurs ^ Any ideas where I am going wrong, this is my first react project any help appreciated!
CSV file format:
Location,TotalCases,Latitude,Longitude
Barking and Dagenham,18,53.546299,-1.46786
Barnet,28,51.605499,-0.207715
What you are trying can be achieved in a much simpler way.
Parse the csv data inside an useEffectHook. You do not need any of these:
const response = await fetch('/data/CovidCasesClean.csv') const reader = response.body.getReader() const result = await reader.read() // raw array const decoder = new TextDecoder('utf-8') const csv = decoder.decode(result.value) // the csv text console.log(csv)
const [data, setData] = useState([]);
useEffect(() => {
Papa.parse(csv, {
download: true, // use this option to interpret the input string as a URL from which to download the input file.
header: true,
skipEmptyLines: true,
complete: results => setData(results.data)
});
}, []);
and once you store the csv parsed markers data loop over them to visualize the markers:
{data &&
data.map(({ Location, Latitude, Longitude, TotalCases }, i) => (
<Marker
key={`markers-${i}`}
position={[Latitude, Longitude]}
icon={icon}
>
<Popup>
<span>
<b>Location</b>: {Location}
<br />
<b>TotalCases</b>: {TotalCases}
</span>
</Popup>
</Marker>
))}