如何在rxJS中展平或合并数组

Question

我有一个结构，我想扁平成一个齐次数组。源数组如下所示：

[
  {
    "countryCode": "CA",
    "countryName": "Canada",
    "states": [
      {
        "stateCode": "CAAB",
        "stateName": "Alberta",
        "countryCode": "CA",
        "stateAbbrev": "AB"
      },
      . . . 
      {
        "stateCode": "CAYT",
        "stateName": "Yukon Territory",
        "countryCode": "CA",
        "stateAbbrev": "YT"
      }
    ]
  },
  {
    "countryCode": "US",
    "countryName": "USA",
    "states": [
      {
        "stateCode": "USAK",
        "stateName": "Alaska",
        "countryCode": "US",
        "stateAbbrev": "AK"
      },
      . . .
      {
        "stateCode": "USWY",
        "stateName": "Wyoming",
        "countryCode": "US",
        "stateAbbrev": "WY"
      }
    ]
  }
]

我想将其转换为应该如下所示：

[
  {
    "value": "CA",
    "label": "Canada"
  },
  {
    "value": "CACB",
    "label": "Alberta"
  },
  . . .
  {
    "value": "CAYT",
    "label": "Yukon Territory"
  },
  {
    "value": "US",
    "label": "USA"
  },
  {
    "value": "USAK",
    "label": "Alaska"
  },
  . . .
  {
    "value": "USWY",
    "label": "Wyoming"
  }
]

到目前为止，我有：

let countries:Observable<ICountry[]> = 
   this.http.get<ICountry[]>(`${this.buildProUrl}/states`);

return countries.map(o => o.map(c => 
  <IStateDropDownItem>{value: c.countryCode, label: c.countryName}));

似乎应该有一种方法将属于每个国家的状态合并到生成的可观察数组中。我已经阅读了concatMap，mergeMap和switchMap文档但我无法弄清楚如何将它们放在一起。

Answer 1

我想你只需要处理结果数组，这可以使用Arry.reduce()函数完成：

const data = [
  {
    "countryCode": "CA",
    "countryName": "Canada",
    "states": [
      {
        "stateCode": "CAAB",
        "stateName": "Alberta",
        "countryCode": "CA",
        "stateAbbrev": "AB"
      },
      {
        "stateCode": "CAYT",
        "stateName": "Yukon Territory",
        "countryCode": "CA",
        "stateAbbrev": "YT"
      }
    ]
  },
  {
    "countryCode": "US",
    "countryName": "USA",
    "states": [
      {
        "stateCode": "USAK",
        "stateName": "Alaska",
        "countryCode": "US",
        "stateAbbrev": "AK"
      },
      {
        "stateCode": "USWY",
        "stateName": "Wyoming",
        "countryCode": "US",
        "stateAbbrev": "WY"
      }
    ]
  }
];

console.log(data.reduce((res, curr) => {
  res.push({value: curr.countryCode, label: curr.countryName});
  return res.concat(curr.states.reduce((res, curr) => {
    res.push({value: curr.stateCode, label: curr.stateName});
    return res;
  }, [])); 
}, []));

如果您使用新的httpClient，那么您的响应已经是一个数组，所以在您的情况下它应该工作：

let countries:Observable<ICountry[]> = 
  this.http.get<ICountry[]>(`${this.buildProUrl}/states`);

return countries.map(o => o.reduce((res, curr) => {
  res.push(<IStateDropDownItem>{value: curr.countryCode, label: curr.countryName});
  return res.concat(curr.states.reduce((res, curr) => {
    res.push(<IStateDropDownItem>{value: curr.stateCode, label: curr.stateName});
    return res;
  }, [])); 
}, []));