Javascript – Generating all combinations of elements in a single array (in pairs)

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Here are some functional programming solutions:

Using EcmaScript2019’s flatMap:

var array = ["apple", "banana", "lemon", "mango"];

var result = array.flatMap(
    (v, i) => array.slice(i+1).map( w => v + ' ' + w )
);

console.log(result);

Before the introduction of flatMap (my answer in 2017), you would go for reduce or [].concat(...) in order to flatten the array:

var array = ["apple", "banana", "lemon", "mango"];

var result = array.reduce( (acc, v, i) =>
    acc.concat(array.slice(i+1).map( w => v + ' ' + w )),
[]);

console.log(result);

Or:

var array = ["apple", "banana", "lemon", "mango"];

var result = [].concat(...array.map( 
    (v, i) => array.slice(i+1).map( w => v + ' ' + w ))
);

console.log(result);

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