Javascript；压缩具有不同值/计数的数组

Question

我得到了一个我正在研究的谜题。我在 Javascript 中得到了一个看起来像这样的多维数组； 每个特征都有一个 ID、一个日期（字符串）和一个状态

例如；

Features = [
    [1, "20200503", "Active"],
    [2, "20200503", "Closed"],
    [2, "20200503", "Closed"],
    [2, "20200502", "Closed"],
    [2, "20200501", "Active"],
    [2, "20200430", "Active"],
    [2, "20200430", "Active"],
    [3, "20200503", "New"],
    [3, "20200502", "New"],
];

我想将此数组压缩成一个我想要的新数组；

Features = [
    [1, 1, "Active"],
    [2, 3, "Closed"],
    [2, 3, "Active"],
    [3, 2, "New"],
];

我想对 ID 和状态进行区分并计算日期。

是否有可能在 Javascript 中做到这一点？

Answer 1

你想要做的是将reduce 数组变成一个更小的数组。好吧，有一个功能！您可以传递一个空数组作为 reduce 函数的第二个参数，以将其用作累加器，并将光标与前一个元素进行比较，以了解如何处理它。

features = features.reduce((acc, cur, index, arr) => {
  let prev = arr[index - 1];

  if (index === 0 || cur[0] !== prev[0] || cur[2] !== prev[2]) acc.push([cur[0], 1, cur[2]]);
  else acc[acc.length - 1][1]++;

  return acc;
}, []);

Answer 2

function compress(features) {
    // First get unique Ids and states
    var ids = new Set(features.map(f => f[0]);
    var states = new Set(features.map(f => f[2]);

    // Array in which we will store the result
    const result = [];

    // Next loop through to make every permutation for the IDs and States 
    for (const id of ids) {
        for (const state of states) {
            // Get number of features with id and state
            let featureCount = features.filter(f => f[0] === id && f[2] === state).length;
            
            // check if there are any with ID "id" and State "state"
            if (featureCount > 0)
                result.push([id, featureCount, state]);
        }
    }
    
    return result;
}

那就这样称呼吧

var compressedFeatures = compress(Features);