当我需要同时过滤多个事物时，如何调用一次filter? [英] How can I call filter once when I need to filter multiple things at the same time?

问题描述

我正在使用lodash进行一些过滤.

I am using lodash to perform some filtering.

我具有以下功能:

filterByCardinalPoint = (key, value) => {
    const { passengersData } = this.props;
    console.log('passengersData', passengersData);
    return filter(passengersData, [key, value]);
  };

  callFilter = () => {
    passengersGoingNorth = this.filterByCardinalPoint('cardinalpoint', 'N')
      .length;
    passengersGoingSouth = this.filterByCardinalPoint('cardinalpoint', 'S')
      .length;
    passengersGoingWest = this.filterByCardinalPoint('cardinalpoint', 'W')
      .length;
    passengersGoingEast = this.filterByCardinalPoint('cardinalpoint', 'E')
      .length;
  };

我正在render方法中调用callFilter.此功能被调用约8次.我该如何优化它才能调用一次?

And I am calling callFilter in the render method. This function is called around 8 times. How can I optimize it so that is call once?

推荐答案

由于您需要各个方向的人数，因此可以使用 _.property() 作为iteratee.分解结果对象以将数字分配给变量.

Since you need the amount of people going in each direction, you can use _.countBy() with _.property() as the iteratee. Destructure the result object to assign the numbers to the variables.

示例:

const { countBy, property } = _;

let passengersGoingNorth, passengersGoingSouth, passengersGoingWest, passengersGoingEast;

const passengersData = [{ cardinalpoint: 'N' }, { cardinalpoint: 'N' }, { cardinalpoint: 'S' }, { cardinalpoint: 'N' }, { cardinalpoint: 'E' }];

({
  N: passengersGoingNorth = 0,
  S: passengersGoingSouth = 0,
  W: passengersGoingWest = 0,
  E: passengersGoingEast = 0
} = countBy(passengersData, property('cardinalpoint')));

console.log(passengersGoingNorth, passengersGoingSouth, passengersGoingWest, passengersGoingEast); // 3, 1, 0, 1

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>

这篇关于当我需要同时过滤多个事物时，如何调用一次filter?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！