TypeScript 类型混淆（TypeError：无法读取未定义的属性“切片”）

我有以下数据csv我的 Angular 项目中的文件也导入了D3.js图书馆：

group,Nitrogen,normal,stress
banana,12,1,13
poacee,6,6,33
sorgho,11,28,12
triticum,19,6,1

我还在打字稿文件中添加了以下代码来显示堆叠栏：

import { Component, OnInit } from '@angular/core';
import * as d3 from 'd3';

@Component({
  selector: 'app-stacked-bar',
  templateUrl: './stacked-bar.component.html',
  styleUrls: ['./stacked-bar.component.css']
})
export class StackedBarComponent implements OnInit {

  data = [
    {"group": "banana", "Nitrogen": "12", "normal": "1", "stress": "13"},
    {"group": "poacee", "Nitrogen": "6", "normal": "6", "stress": "33"},
    {"group": "sorgho", "Nitrogen": "11", "normal": "28", "stress": "12"},
    {"group": "triticum", "Nitrogen": "19", "normal": "6", "stress": "1"}
  ];

  svg: any;

  margin = 50;
  width = 750 - (this.margin * 2);
  height = 400 - (this.margin * 2);

  ngOnInit(): void {

    this.createSvg();
    this.drawBars(this.data);
  }

  createSvg(): void {

    this.svg = d3.select("figure#stacked-bar")
    .append("svg")
    .attr("width", this.width + (this.margin * 2))
    .attr("height", this.height + (this.margin * 2))
    .append("g")
    .attr("transform", "translate(" + this.margin + "," + this.margin + ")");
  }

  drawBars(data): void {
 
    // List of subgroups - Header of the csv file.
    // ["Nitrogen", "normal", "stress"]
    const subgroups = data.columns.slice(1);
            
    // List of groups - Value of the first column, called group.
    const groups = data.map(d => (d.group));

    // Create the X-axis band scale.
    const x = d3.scaleBand()
    .domain(groups)
    .range([0, this.width])
    //.domain(data.map(d => d.groups))
    .padding(0.2);

    // Draw the X-axis on the DOM.
    this.svg.append("g")
    .attr("transform", "translate(0," + this.height + ")")
    .call(d3.axisBottom(x).tickSizeOuter(0));
    
    // Create the Y-axis band scale.
    const y = d3.scaleLinear()
    .domain([0, 60])
    .range([this.height, 0]);

    // Draw the Y-axis on the DOM.
    this.svg.append("g")
    .call(d3.axisLeft(y));

    // color palette = one color per subgroup
    const color = d3.scaleOrdinal()
    .domain(subgroups)
    .range(['#e41a1c','#377eb8','#4daf4a']);

    // Stack the data per subgroup.
    const stackedData = d3.stack()
    .keys(subgroups)
    (data);

    // Create and fill the bars.
    this.svg.append("g")
    .selectAll("g")
    .data(stackedData)
    .join("g")
    .attr("fill", d => color(d.key))
    .selectAll("rect")    
    .data(d => d)
    .join("rect")
    .attr("x", d => x(d.data.group))
    .attr("y", d => y(d[1]))
    .attr("height", d => y(d[0]) - y(d[1]))
    .attr("width", x.bandwidth());
  }
}

但我只得到一块空地。当我检查页面时，出现以下控制台错误：

类型错误：无法读取未定义的属性“切片”

由于某些类型的歧义data, the slice方法无法应用，但是当我只是复制和粘贴时["Nitrogen", "normal", "stress"]代替subgroups在代码中，一切正常！

有人可以帮我解决这个问题吗？

附注图表应如下所示：

假设你正在这样做example https://www.d3-graph-gallery.com/graph/barplot_stacked_basicWide.html，然后注意这使用d3.csv将 csv 输入转换为对象数组。 D3 创建这个数组plus一个习俗columns示例中使用的属性。

const csv = `group,Nitrogen,normal,stress
banana,12,1,13
poacee,6,6,33
sorgho,11,28,12
triticum,19,6,1`;

const data = d3.csvParse(csv);
console.log(data.columns);

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/4.13.0/d3.min.js"></script>

在您的代码中，您有相同的对象数组，但您没有显示 csv 导入方法，因此我们可能假设您没有使用d3.csv并使用其他方法来获取数据。

在这种情况下，相当于data.columns is Object.keys(data[0])。从那里你可以使用slice获取要为堆栈分组的列：

const data = [
  {"group": "banana", "Nitrogen": "12", "normal": "1", "stress": "13"},
  {"group": "poacee", "Nitrogen": "6", "normal": "6", "stress": "33"},
  {"group": "sorgho", "Nitrogen": "11", "normal": "28", "stress": "12"},
  {"group": "triticum", "Nitrogen": "19", "normal": "6", "stress": "1"}
];

const dataColumns = Object.keys(data[0]);
console.log(dataColumns);

const subgroups = dataColumns.slice(1)
console.log(subgroups);