How to replace array element with respect to Index on another array

Question

I have one array which contains values array1 = [a,b,c,d,e,f,g] and another array contains index of array1 and the value to be replaced array2 = [[2,u],[3,x],[6,z]].

Now I want to replace value of array1 with respect to array2 please not array2 consist of [array1_position, value_to_be_replaced]

Now my new arra1 should look like this array1 = [a,b,u,x,e,f,z].

I can do this with for loop but its again time consuming. what trick can i use to replace the value quickly. I am just learning about arrays and have a little knowledge on it.

just as @Ramesh said, you will have to do a loop regardless of the syntax and even the language itself. That being said the best runtime complexity u can get is O(array2.length), and that is my looping through array2 items and making the needed changes from there — ehab
– ehab, Commented May 30, 2020 at 9:49

icebug · Accepted Answer · 2020-05-30 09:49:43Z

1

I don't think there is any shorthand for such a verbose question. Something on top of my mind is

array2.forEach((el) => {
  array1[el[0]] = el[1];
})

answered May 30, 2020 at 9:49

icebug

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ehab · Accepted Answer · 2020-05-30 09:45:51Z

1

you could do this

array2.forEach(arr => {
   const [index, replaced] = arr;
   array1[index] = replaced;
});

answered May 30, 2020 at 9:45

ehab

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Comments

Rajneesh · Accepted Answer · 2020-05-30 09:48:31Z

1

You can take fromEntries of the other array then just map it:

var array1 = ['a','b','c','d','e','f','g'];
var array2 = [[2,'u'],[3,'x'],[6,'z']];
var d=Object.fromEntries(array2);
var result = array1.map((val, i)=> d[i] || val);
console.log(result);

answered May 30, 2020 at 9:48

Rajneesh

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2 Comments

Mask Over a year ago

what if my array2 = [2,'u','xyz'],[3,'x'],[6,'z'] and I need to do the same thing.

Rajneesh Over a year ago

@Mask, It won't work then beacuse fromEntries works on key value pair, so in your case it will discard the xyz and take u and then create object.

Nina Scholz · Accepted Answer · 2020-05-30 10:05:01Z

1

With an ordered array2 by indices, you could take a closure over an index of this array and map the values from eithe the first array or the replacements array.

var array1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g'],
    array2 = [[2, 'u'], [3, 'x'], [6, 'z']],
    result = array1.map(
        (j => (v, i) => i === array2[j][0] ? array2[j++][1] : v)
        (0)
    );

console.log(result);

answered May 30, 2020 at 10:05

Nina Scholz

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1 Comment

ehab Over a year ago

if array1 is extremely larger than array2 then performance will suffer, its better to loop through array2 and modify array1 in place for best runtime/memory performance.

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