Removing words from array using regex

Question

I am creating a program that involves removing text from an array. If a letter is included in a word in the array, then that word will be removed. My first test was successful, a simple regular expression with a small array:

var regex = /z/;
var words = ["eggs", "zebras", "lampshade"];

for (i = 0; i < words.length; i++) {
  let testResult = regex.test(words[i]);

  if (!testResult) {
    words.splice(i, 1);
  }
}
console.log(words);

As expected, it returned [ 'zebras' ]. Because this was successful, I quickly scaled up using an npm package called "an-array-of-english-words". I ran my new script:

const masterWords = require("an-array-of-english-words");
var regex = /z/;
var words = masterWords;

for (i = 0; i < words.length; i++) {
  let testResult = regex.test(words[i]);

  if (!testResult) {
    words.splice(i, 1);
  }
}
console.log(words);

Every time I run it it ends up returning values that do not abide by the regular expression. For example, the code above returned ['aa', 'aahed', 'aahs', ...] as its first few values. Do I have to change my code to deal with a bigger array? Am I making a stupid mistake I didn't notice?

Can you try using it like this ? console.log(words.filter(d => /z/.test(d))) — Harmandeep Singh Kalsi
– Harmandeep Singh Kalsi, Commented May 24, 2020 at 14:21

Igor Moraru · Accepted Answer · 2020-05-24 14:27:27Z

1

I think it may be due to the fact that you are splicing the array and looping it at the same time.

For ex. if the length of array is 5 and the current index is 2, after splicing the array, the item at the index 3 will be moved to the index 2, and will be skipped in the next iteration, since the next index will be 3.

So, you can create a clone of the words and change it, while iterating the original array.

answered May 24, 2020 at 14:27

Igor Moraru

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1 Comment

Zimri Leijen Over a year ago

Yes, you can verify this by trying this array: ['a', 'a', 'z', 'a', 'a'] You'll see ['a', 'z', 'a'] It seems every false value will let through the next value, regardless if it's true or false.

Harmandeep Singh Kalsi · Accepted Answer · 2020-05-24 14:32:30Z

0

@Joey , in official documentation if you see , try using it this way as a workaround . Also @Igor Moraru's answer explains why the issue might be happening.

console.log(words.filter(d => /z/.test(d)))

edited May 24, 2020 at 14:32

answered May 24, 2020 at 14:26

Harmandeep Singh Kalsi

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