javascript - 将数组拆分为从负到正的范围

Question

目前我有一个levels包含其他数组的数组level，这些数组包含stages.

我想用一个名为position. 该位置返回到数组中心的距离。中心是指长度 / 2。

如果数组长度是偶数，我想要以下范围

... -3.5 , -2.5 , -1.5 , -0.5 , 0.5 , 1.5 , 2.5 , 3.5 ...

如果数组长度甚至不是我想要以下范围

... -4 , -3 , -2 , -1 , 0 , 1 , 2 , 3 , 4 ...

我开始创建这个

const distanceLevels = [
  [{
    "id": 1
  }, {
    "id": 8
  }],
  [{
    "id": 2
  }],
  [{
    "id": 3
  }, {
    "id": 4
  }, {
    "id": 5
  }, {
    "id": 7
  }],
  [{
    "id": 6
  }]
];

function getViewLevels() {
  const viewLevels = []; // the new array as the result

  distanceLevels.forEach(level => { // one level containing the stages
    const levelLength = level.length;
    const halfLevelLength = levelLength * 0.5;
    const levelLengthIsEven = levelLength % 2 == 0;

    let viewLevel = []; // the mapped level

    if (levelLengthIsEven) {
      addViewStage(viewLevel, level[Math.floor(halfLevelLength)], 0);
    }

    for (let i = 0; i < halfLevelLength; i++) {
      let rightPosition = i - halfLevelLength;
      let leftPosition = i;
      let leftStageIndex = i;

      if (levelLengthIsEven) {
        leftPosition++;
        leftStageIndex += Math.floor(halfLevelLength) + 1;
      } else {
        rightPosition += 0.5;
        leftPosition += 0.5;
        leftStageIndex += halfLevelLength;
      }

      addViewStage(viewLevel, level[i], rightPosition);
      addViewStage(viewLevel, level[leftStageIndex], leftPosition);
    }

    viewLevel = viewLevel.sort((a, b) => a.position > b.position); // sort the result by their position, means from negative to positive
    viewLevels.push(viewLevel); // add this new view level
  });

  console.log(viewLevels); // <---- result here!
}

function addViewStage(viewLevel, stage, position) { // push a new element to the array
  viewLevel.push({
    stage: stage,
    position: position
  });
}

getViewLevels();

这是我得到的结果

我真的在数学上挣扎。我要做的就是将每个对象映射到级别

舞台（对象）

至

{
   stage: stage,
   position: position // with the correct range
}

标签： javascriptarrays

Answer 1

您可以使用两个嵌套来做到这一点maps：

const distanceLevels = [
  [{
    "id": 1
  }, {
    "id": 8
  }],
  [{
    "id": 2
  }],
  [{
    "id": 3
  }, {
    "id": 4
  }, {
    "id": 5
  }, {
    "id": 7
  }],
  [{
    "id": 6
  }]
]

const mappedLevels = distanceLevels.map(level =>
  level.map((stage, index, lvl) => (
    {...stage, position: index - (lvl.length - 1) / 2}
  ))
);

console.log(mappedLevels);