# JavaScript : Create an array of elements, grouped based on the position in the original arrays and using function as the last value to specify how grouped values should be combined

## JavaScript fundamental (ES6 Syntax): Exercise-100 with Solution

Write a JavaScript program to create an array of elements, grouped based on the position in the original arrays and using function as the last value to specify how grouped values should be combined.

Note: Check if the last argument provided is a function.

• Check if the last argument provided is a function.
• Use Math.max() to get the longest array in the arguments.
• Use Array.from() to create an array with appropriate length and a mapping function to create array of grouped elements.
• If lengths of the argument arrays vary, undefined is used where no value could be found.
• The function is invoked with the elements of each group.

Sample Solution:

JavaScript Code:

``````//#Source https://bit.ly/2neWfJ2
const zipWith = (...array) => {
const fn = typeof array[array.length - 1] === 'function' ? array.pop() : undefined;
return Array.from(
{ length: Math.max(...array.map(a => a.length)) },
(_, i) => (fn ? fn(...array.map(a => a[i])) : array.map(a => a[i]))
);
};

zipWith([1, 2], [10, 20], [100, 200], (a, b, c) => a + b + c); // [111,222]

console.log(zipWith(
[1, 2, 3],
[10, 20],
[100, 200],
(a, b, c) => (a != null ? a : 'a') + (b != null ? b : 'b') + (c != null ? c : 'c')
));
```
```

Sample Output:

```[111,222,"3bc"]
```

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-100-1 by w3resource (@w3resource) on CodePen.

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## JavaScript: Tips of the Day

How to remove a specific item from an array?

Find the index of the array element you want to remove using indexOf, and then remove that index with splice.

The splice() method changes the contents of an array by removing existing elements and/or adding new elements.

```const array = [2, 5, 9];

console.log(array);

const index = array.indexOf(5);
if (index > -1) {
array.splice(index, 1);
}

// array = [2, 9]
console.log(array);```

The second parameter of splice is the number of elements to remove. Note that splice modifies the array in place and returns a new array containing the elements that have been removed.

For the reason of completeness, here are functions. The first function removes only a single occurrence (i.e. removing the first match of 5 from [2,5,9,1,5,8,5]), while the second function removes all occurrences:

```function removeItemOnce(arr, value) {
var index = arr.indexOf(value);
if (index > -1) {
arr.splice(index, 1);
}
return arr;
}

function removeItemAll(arr, value) {
var i = 0;
while (i < arr.length) {
if (arr[i] === value) {
arr.splice(i, 1);
} else {
++i;
}
}
return arr;
}
//Usage
console.log(removeItemOnce([2,5,9,1,5,8,5], 5))
console.log(removeItemAll([2,5,9,1,5,8,5], 5))
```

Ref: https://bit.ly/2N9nKRp