How can you concatenate or group multiple strings within the same array?-CodePudding

If given an array of elements let array = ['apple', 'banana', 'salami', 'cheese']

What is the best practice to get this result : ['applebanaa' , 'salamicheese']

My first thought was to use reduce which works but it concatenates every string into one long string. See example below

```let array = ['apple', 'banana', 'salami', 'cheese']"

array.reduce((a,b) => a   b);

output : applebanaasalamicheese```

I feel like I am on the right track here. Maybe I need to do something to the equation within the parenthesis of reduce to get the result I am looking for?

I am relatively new to Javascript, but I hope that this question is clear enough to follow. Thanks in advance for any help!

Best Regards

CodePudding user response：

reduce will be very slightly unwieldly here. The output structure is an array of strings that isn't one-to-one with the input, and the desired output isn't a number or primitive. Easier to create a variable outside the loop and push to it than to return the same accumulator array each time.

A plain for loop that iterates over indicies i and i 1 at a time would work.

const array = ['apple', 'banana', 'salami', 'cheese'];
const output = [];
for (let i = 0; i < array.length; i  = 2) {
  output.push(array[i]   (array[i   1] || ''));
}
console.log(output);

If you really wanted to use .reduce...

const array = ['apple', 'banana', 'salami', 'cheese'];
const output = array.reduce((a, str, i) => {
  if (i % 2 === 0) {
    a.push(str);
  } else {
    a[a.length - 1]  = str;
  }
  return a;
}, []);
console.log(output);

CodePudding user response：

You can use Array.prototype.reduce() combined with Array.prototype.concat()

Code:

const array = ['apple', 'banana', 'salami', 'cheese']

const result = array.reduce((a, c, i, arr) => 
  a.concat(i % 2 === 0 ? [c   (arr[i   1] || '')] : []), [])

console.log(result)

Also you can use Array.prototype.filter() combined with Array.prototype.map()

Code:

const array = ['apple', 'banana', 'salami', 'cheese']

const result = array
  .filter((_, index) => index % 2 === 0)
  .map((item, index) => item   (array[index * 2   1] || ''))

console.log(result)

CodePudding user response：

if you only want to join strings you can use array.join()

const sampleArray = ['apple', 'banana', 'salami', 'cheese']
const joinedArray = SampleArray.join(' ') // "apple banana salmi cheese"

you can choose space (' ') or comma for the separator, see here for the docs Array.join()

CodePudding user response：

It appears that the patterns you are looking for is chunk(2) and map(join('')) chunk is available with lodash among other libraries, or you can implement it yourself.

// If given an array of elements let array = ['apple', 'banana', 'salami', 'cheese']
// What is the best practice to get this result : ['applebanaa' , 'salamicheese']

const array = ['apple', 'banana', 'salami', 'cheese'];

// https://lodash.com/docs/4.17.15#chunk
// https://stackoverflow.com/questions/8495687/split-array-into-chunks
function chunk(array, size = 1) {
  let chunked = [];
  for (let i = 0; i < array.length; i =size) {
    chunked.push(array.slice(i, i size));
  }
  return chunked;
}

/* Chunk will divide up the array in to size batches
 * and return an array of arrays of elements of the
 * chunk size.
 */

// const chunked = chunk(array, 2);
// chunked = [['apple', 'banana'], ['salami', 'cheese']];

// Here is the final expression
console.log(
  chunk(array, 2)
    .map(chunk => chunk.join(''))
);