我正在尝试遍历已从Locations和Lat / Lng对的CSV文件解析的对象。但是,当我循环遍历此对象时,第一个循环将返回所有值为undefined的对象。我的代码如下:
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>
)
}
运行控制台行:<div>{console.log(data.key, data.location, data.latitude, data.longitude, data.cases)}</div>
时,第一个结果返回:
未定义未定义未定义未定义
而第二次遍历将返回正确的对象,如下所示:
0吠叫和达格纳姆53.546299 -1.46786 18
这会导致我创建标记对象失败,因为第一个对象不是latlng对,我一直在尝试像这样创建标记:
<Marker position={(data.longitude, data.latitude)}>
<Popup>
<span>
A pretty CSS3 popup.
<br />
Easily customizable.
</span>
</Popup>
</Marker>;
这是发生错误的地方^任何想法,我要去哪里错了,这是我的第一个反应项目,感谢任何帮助!
CSV文件格式:
Location,TotalCases,Latitude,Longitude
Barking and Dagenham,18,53.546299,-1.46786
Barnet,28,51.605499,-0.207715
您正在尝试的事情可以通过更简单的方法来实现。
解析useEffectHook中的csv数据。您不需要任何这些:
常量响应=等待fetch('/ data / CovidCasesClean.csv')const reader = response.body.getReader()const result = await reader.read()//原始数组const解码器=新的TextDecoder('utf-8')const csv = coder.decode(result.value)// csv文本console.log(csv)
const [data, setData] = useState([]);
useEffect(() => {
async function getData() {
Papa.parse(csv, {
download: true,
header: true,
skipEmptyLines: true,
complete: results => setData(results.data)
});
}
getData();
}, []);
并且一旦存储了csv解析的标记数据,它们就会循环遍历以使标记可视化:
{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>
))}