How do you split an array into array pairs in Java

问题:

I want to split an array into pairs of arrays

so var arr=[2,3,4,5,6,4,3,5,5]

would be newarr =[[2,3],[4,5],[6,4],[3,5],[5]]

回答1:

You can use js reduce

initialArray.reduce(function(result, value, index, array) {
  if (index % 2 === 0)
    result.push(array.slice(index, index + 2));
  return result;
}, []);

回答2:

There's no pre-baked function to do that, but here's a simple solution:

var splitPairs = function(arr) {
    var pairs = [];
    for (var i=0 ; i<arr.length ; i+=2) {
        if (arr[i+1] !== undefined) {
            pairs.push ([arr[i], arr[i+1]]);
        } else {
            pairs.push ([arr[i]]);
        }
    }
    return pairs;
};

回答3:

Lodash has a method for this: https://lodash.com/docs/4.17.10#chunk

_.chunk([2,3,4,5,6,4,3,5,5], 2); // => [[2,3],[4,5],[6,4],[3,5],[5]]

回答4:

Yet another that's a bit of a mish-mash of the already-posted answers. Adding it because having read the answers I still felt things could be a little easier to read:

var groups = [];

for(var i = 0; i < arr.length; i += 2)
{
    groups.push(arr.slice(i, i + 2));
}

回答5:

A slightly different approach than using a for loop for comparison. To avoid modifying the original array slice makes a shallow copy since JS passes objects by reference.

function pairArray(a) {
  var temp = a.slice();
  var arr = [];

  while (temp.length) {
    arr.push(temp.splice(0,2));
  }

  return arr;
}

var array = [2,3,4,5,6,4,3,5,5];
var newArr = pairArray(array);

function pairArray(a) {
  var temp = a.slice();
  var arr = [];

  while (temp.length) {
    arr.push(temp.splice(0,2));
  }

  return arr;
}

document.write('<pre>' + JSON.stringify(newArr) + '</pre>');

回答6:

I would use lodash for situations like this.

Here is a solution using _.reduce:

var newArr = _(arr).reduce(function(result, value, index) {
  if (index % 2 === 0)
    result.push(arr.slice(index, index + 2));

  return result;
}, []);

var arr = [2,3,4,5,6,4,3,5,5];

var newArr = _(arr).reduce(function(result, value, index) {
  if (index % 2 === 0)
    result.push(arr.slice(index, index + 2));
  
  return result;
}, []);

document.write(JSON.stringify(newArr)); // [[2,3],[4,5],[6,4],[3,5],[5]]

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.10.0/lodash.min.js"></script>

回答7:

Here's another solution using lodash helpers:

function toPairs(array) {
  const evens = array.filter((o, i) => i % 2);
  const odds = array.filter((o, i) => !(i % 2));
  return _.zipWith(evens, odds, (e, o) => e ? [o, e] : [o]);
}
console.log(toPairs([2,3,4,5,6,4,3,5,5]));

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.13.1/lodash.min.js"></script>

回答8:

It's possible to group an array into pairs/chunks in one line without libraries:

function chunks(arr, size = 2) {
  return arr.map((x, i) => i % size == 0 && arr.slice(i, i + size)).filter(x => x)
}
console.log(chunks([1, 2, 3, 4, 5, 6, 7])) // -> [[1, 2], [3, 4], [5, 6], [7]]

回答9:

Here's a good generic solution:

function splitInto(array, size, inplace) {
    var output, i, group;

    if (inplace) {
        output = array;

        for (i = 0; i < array.length; i++) {
            group = array.splice(i, size);

            output.splice(i, 0, group);
        }
    } else {
        output = [];

        for (i = 0; i < array.length; i += size) {
            output.push(array.slice(i, size + i));
        }
    }

    return output;
}

For your case, you can call it like this:

var arr= [2,3,4,5,6,4,3,5,5];
var newarr = splitInto(arr, 2);

The inplace argument determines whether the operation is done in-place or not.

Here's a demo below:

function splitInto(array, size, inplace) {
    var output, i, group;

    if (inplace) {
        output = array;

        for (i = 0; i < array.length; i++) {
            group = array.splice(i, size);

            output.splice(i, 0, group);
        }
    } else {
        output = [];

        for (i = 0; i < array.length; i += size) {
            output.push(array.slice(i, size + i));
        }
    }

    return output;
}

var arr= [2,3,4,5,6,4,3,5,5];
var newarr = splitInto(arr, 2);

disp(newarr);

// or we can do it in-place...
splitInto(arr, 3, true);

disp(arr);

function disp(array) {  
  var json = JSON.stringify(array);

  var text = document.createTextNode(json);
  var pre = document.createElement('pre');

  pre.appendChild(text);
  document.body.appendChild(pre);
}

回答10:

const items = [1,2,3,4,5];

const createBucket = (bucketItems, bucketSize) => buckets => { return bucketItems.length === 0 ? buckets : [...buckets, bucketItems.splice(0, bucketSize)]; };

const bucketWithItems = items.reduce(createBucket([...items], 4), []);

回答11:

There is now the flexible Array#flatMap(value, index, array):

const pairs = arr.flatMap((_, i, a) => i % 2 ? [] : [a.slice(i, i + 2)]);

And the possibly more efficient, but goofy looking Array.from(source, mapfn?):

const pairs = Array.from({ length: arr.length / 2 }, (_, i) => arr.slice(i * 2, i * 2 + 2))

回答12:

Here is a short and more generic solution:

function splitArrayIntoPairs(arr, n) {
 var len = arr.length
  var pairs = []

  for (let i = 0; i < len; i += n) {
    var temp = []
    for (var j = i; j < (i + n); j++) {
      if (arr[j] !== undefined) {
        temp.push(arr[j])
      }
    }
    pairs.push(temp)
  }
  return pairs
}

Where arr is your array and n is no of pairs