Replacing an item in an array with another item in Javascript

Question

I have an array like this:

  var CutRoadArray = [
            ['Location', '_Location'],
            ['Applicant Info', '_ApplicantInfo'],
            ['Details', '_ApplicationDetails'],
            ['Bond Info', '_BondInfo'],
            ['Attachments', '_Attachments'],
            ['Review', '_ReviewA']
        ];

I am trying to replace the last item, with a different entry.

The code I have so far goes like below:

                var newreviewElem = ['Review', '_ReviewB'];
                var index = CutRoadArray.lastIndexOf('_ReviewA');
                CutRoadArray.splice(index, 0, newreviewElem);
                console.log(CutRoadArray);

This is however not working. What am I doing wrong ?

https://jsfiddle.net/yygLdo0o/

Blunderfest · Accepted Answer · 2015-08-25 17:14:35Z

1

There are actually two things wrong with your answer.

The first is that you need to grab the correct index. If you're replacing the last item, just grab the array.length.

The second is that you need to indicate how many you're replacing:

CutRoadArray.splice(CutRoadArray.length - 1, 1, newreviewElem);

The second argument in splice should be 1, not 0.

This will replace the last element of any size array, because it doesn't rely on an item in the array being in a specific location or a particular index.

CutRoadArray.length - 1 is grabbing the number of items in the array, but since splice uses a zero based index, you have to subtract one to get the index of the last item in the array.

The second argument (bolded below), tells splice to replace a single item.

Documentation about splice

CutRoadArray.splice(CutRoadArray.length - 1, 1, newreviewElem);

And then finally, the last argument is the item to actually add to the array.

Working fiddle

edited Aug 25, 2015 at 17:14

answered Aug 25, 2015 at 17:07

Blunderfest

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2 Comments

w2olves Over a year ago

Thank you and yes, this works, can you please explain the CutRoadArray.splice(CutRoadArray.length - 1, 1, newreviewElem); part so me or anyone else who stumbles across this, would learn ?

w2olves Over a year ago

thank you for the array 101, I hope this helps others as well.

GPicazo · Accepted Answer · 2015-08-25 17:02:58Z

1

It should be:

CutRoadArray.splice(index, 1, newreviewElem);

The second parameter indicates how many items should be replaced.

answered Aug 25, 2015 at 17:02

GPicazo

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1 Comment

w2olves Over a year ago

Thank you for your swift help.

Igor · Accepted Answer · 2015-08-25 17:05:21Z

1

Your

CutRoadArray.lastIndexOf('_ReviewA');

will, of course, not find anything since CutRoadArray contains arrays, not strings.

for(var iter = 0; iter < CutRoadArray.length; iter++) {
  if (CutRoadArray[iter][1] == '_ReviewA') {
    CutRoadArray[iter] = newreviewElem;
    break;
  }
}

answered Aug 25, 2015 at 17:05

Igor

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Comments

doldt · Accepted Answer · 2015-08-25 17:09:14Z

1

If you want to replace the element, use

CutRoadArray.splice(index, 1, newreviewElem);

The second parameter of splice is the deleteCount, 0 means no item will be removed.

An other problem with your code is that

CutRoadArray.lastIndexOf('_ReviewA');

will always return -1, as CutRoadArray is an array of arrays, meaning every element of it is an array, it doesn't have an element which is '_ReviewA'. (That's an element of one of CutRoadArray's elements.)

edited Aug 25, 2015 at 17:09

answered Aug 25, 2015 at 17:02

doldt

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3 Comments

w2olves Over a year ago

What would be the right way to do this. Lets say I have a button or a checkbox, depending on its state, it would alter the element to reviewA or reviewB ?

doldt Over a year ago

@user3067743 it's hard to tell what's the right way to do this without knowing more of your use-case. You will probably have to look through all the elements of the array to find one containing your string.

w2olves Over a year ago

the part in brackets, (That's an element of one of CutRoadArray's elements.) finally sunk in, your answer was swift and correct, I am accepting Blunderfest's answer only because it has a fiddle, someone wandering into this page could easily try the fiddle. Thank you ...

Nina Scholz · Accepted Answer · 2015-08-25 17:25:46Z

I suggest to iterate over the main array and search in the nested array for the wanted index. After found it is simple to replace the nested array at the index like array[index] = replace;. If not found, the the array is pushed to the end.

function replace(array, find, replace) {
    var index;
    if (array.some(function (a, i) {
            if (~a.indexOf(find)) {
                index = i;
                return true;
            }
        })
    ) {
        array[index] = replace;
    } else {
        array.push(replace);
    }
}

var cutRoadArray = [
      ['Location', '_Location'],
      ['Applicant Info', '_ApplicantInfo'],
      ['Details', '_ApplicationDetails'],
      ['Bond Info', '_BondInfo'],
      ['Attachments', '_Attachments'],
      ['Review', '_ReviewA']
];

replace(cutRoadArray, '_ReviewA', ['Review', '_ReviewB']);
document.write('<pre>' + JSON.stringify(cutRoadArray, 0, 4) + '</pre>');

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