Elementwise concatenation of string arrays

Question

I am looking for a JavaScript function which accepts two string arrays of equal length and outputs a single string array which is the same length as the input arrays, containing the element-wise-concatenated strings of the input arrays. Is there a built-in JavaScript function which does this?

Additionally, I would like to add in a string between the concatenated elements when the element-wise concatenation is done. For example, so that this would be true for each i:

outputArray[i] = inputArray1[i] + " - " + inputArray2[i]

From the sample you posted you already have a solution that would work, if you are looping over the input array — Adam H
– Adam H, Commented Aug 2, 2018 at 18:58
Step 1: Take the code you have working now and move it into a function Step 2: call that function Step 3: Profit — Adam H
– Adam H, Commented Aug 2, 2018 at 19:06
There's no in-built one to perform specifically this action. It's known as a zip. The closest thing in the js standard library is a reduce like Nina has posted. There's no reason why you couldn't make your own zip function. — Dan
– Dan, Commented Aug 2, 2018 at 19:12

Nina Scholz · Accepted Answer · 2018-08-02 19:12:53Z

7

You could reduce an array with the single arrays. This works for more than one array as well.

var inputArray1 = ['abc', 'def', 'ghi'],
    inputArray2 = ['3', '6', '9'],
    outputArray = [inputArray1, inputArray2].reduce((a, b) => a.map((v, i) => v + ' - ' + b[i]));

console.log(outputArray);

More functional

var inputArray1 = ['abc', 'def', 'ghi'],
    inputArray2 = ['3', '6', '9'],
    outputArray = [inputArray1, inputArray2]
        .reduce((a, b) => a.map((v, i) => [].concat(v, b[i]))) // get single parts
        .map(a => a.join(' - '));                              // join inner arrays

console.log(outputArray);

edited Aug 2, 2018 at 19:12

answered Aug 2, 2018 at 19:08

Nina Scholz

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5 Comments

Sivcan Singh Over a year ago

He asked for a function so: concatStrings = (a, b) => { return [a, b].reduce((a, b) => a.map((v, i) => v + '-' + b[i])); }

Josh Withee Over a year ago

That's exactly what I'm looking for! Thanks. My primary need was for a one-liner that would be easy to use in the Chrome Dev Tools javascript console

Adam H Over a year ago

@Marathon55 just an FYI you can run multiline scripts in Chrome Dev Tools Console, I do it all the time. This is unrelated to your question or answer but just a little tidbit I thought I would pass on.

dennlinger Over a year ago

Is there any specific reason why we need the .reduce() as well? In my opinion, the function itself can work simply with the map, right? Like merge = (a,b) => {return a.map(val, ind) => val + "-" + b[ind]);}

Nina Scholz Over a year ago

right, with map it would work to, but it needs to address the other array inside of the callback. a better approach is to collect all necessary array in another array and get the result from this array, because it it easily to extend with more arrays,

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