Question 51826 in Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript, return all the indexes that match substrings in original array;

I have an array that I wish to return the indexes in a new array if the original array matches a substring.

Currently I am coding it like this:

tv_show = ["bbc1_7.30","bbc1_8.00","itv1_8.40","bbc1_10.00"];
    indexesFromSearch = [];

tv_show.forEach(function(elem, index, array){
    a0 = tv_show[index].substring(0,5);
    if(a0=="bbc1_"){ 
        indexesFromSearch.push(index);
    };
    return indexesFromSearch;
});

alert(indexesFromSearch);

It works fine but just wondered if there is a better way to code it.

Thanks.

Tags:

4

Answers


  1. 0

    You could get the indices and filter with startsWith.

    const
    tv_show = ["bbc1_7.30", "bbc1_8.00", "itv1_8.40", "bbc1_10.00"],
    indices = [...tv_show.keys()].filter(i => tv_show[i].startsWith('bbc1_'));

console.log(indices);
    Login or Signup to reply.
  2. 0

    you can use includes like this:

    tv_show = ["bbc1_7.30", "bbc1_8.00", "itv1_8.40", "bbc1_10.00"];
indexesFromSearch = [];

tv_show.forEach((e, index) => {
  tv_show[index].includes("bbc1_") && indexesFromSearch.push(index);
  return indexesFromSearch;
});

alert(indexesFromSearch);
    Login or Signup to reply.
  3. 0

    The simplest way to achieve this is to reduce the array. This is essentially a combination of filter and map.

    const
  tv_show = ['bbc1_7.30', 'bbc1_8.00', 'itv1_8.40', 'bbc1_10.00'],
  indexesFromSearch = tv_show.reduce((acc, val, index) => {
    if (val.startsWith('bbc1_')) {
      acc.push(index);
    }
    return acc;
  }, []);

console.log(indexesFromSearch);

    Here is a concise version with a reusable helper:

    const pushIf = (arr, val, predicate, alt) => {
  if (predicate(val)) arr.push(alt ?? val);
  return arr;
};

const
  tv_show = ['bbc1_7.30', 'bbc1_8.00', 'itv1_8.40', 'bbc1_10.00'],
  indexesFromSearch = tv_show.reduce((acc, val, index) =>
    pushIf(acc, val, v => v.startsWith('bbc1_'), index), []);

console.log(indexesFromSearch);
    Login or Signup to reply.
  4. 0

    You can use reduce and startsWith :

    const tv_show = ["bbc1_7.30", "bbc1_8.00", "itv1_8.40", "bbc1_10.00"];

const indexes = tv_show.reduce((acc, curr, idx) => curr.startsWith("bbc1_") ? [...acc, idx] : acc, []);
console.log(indexes);
    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search